# Effect of Manganese Ions on Spectroscopic and Insulating Properties of Aluminophosphate Glasses

Authors: B. Kassa; J. Leta Tesfaye; B. Bulcha; R. Kiran; T. Deepak; Dayanand Lal; S. Venkatesh; R. Krishnaraj
Journal: Advances in Materials Science and Engineering
 (2021)

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## Abstract

The melt-quenching technique was used to produce 39CdO–10Al2O3-(51-x) P2O5: xMnO glasses (x = 0, 0.1, 0.2, 0.3, and 0.4 wt.%). Various stability factors were calculated and presented from DTA analysis. The stability of the glass network appears to increase with the increase of MnO concentration, according to the findings. IR spectral analysis of these glasses exhibited several symmetrical and asymmetrical bands due to phosphate groups. The observed change in these band intensities with the rise in MnO concentrations, ranging from 0.1 wt.% to 0.4 wt.%, shows an increase in the stability of the glass network. Optical absorption analyses of these glasses revealed an absorption band that shifted from 500 to 488 nm as the concentration of manganese oxide (MnO) increased from 0.1 wt.% to 0.4 wt.%, indicating that Mn2+ ions were gradually converted into Mn3+ ions. EPR spectra of these glasses were characterized by two signals due to Mn2+ and Mn3+ ions. Observations on these signal intensity variations revealed an increase in stability of the glass network with the increase of MnO concentration from 0.1 wt.% to 0.4 wt.%. Parameters, which describe the insulating characteristics, for example, dielectric constant, ε, dielectric loss, tan δ, and AC conductivity σac, were determined in relation to frequency (103 Hz to 105 Hz) and temperature (20°C to 400°C) and presented in the dielectric analysis of these glasses.


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## Body

## 1. Introduction

The dielectric constant, loss tan, and AC conductivity, as well as the dielectric breakdown strength of the glasses, are used to determine their insulating character and understand the structural features over such a wide frequency and temperature range [1]. In recent years, a number of studies have investigated a number of inorganic glasses under this way, resulting in useful information [1–3].Phosphate glasses may be used for a variety of uses, including bone transplantation, hazardous waste containment, high electron conductors, laser host components, low-temperature seals, metallic seal materials, bioglasses, diametric purposes, and solid state electrolytes, among others [4–7]. They have significant physical properties, such as a low melting temperature, high heat transfer coefficient, high ultraviolet transmission, lower glass transition temperature, minimum softening temperature, high ionic conductivity, and biocompatibility [8]. Addition of Al2O3 to phosphate glasses improves their chemical durability and modifies their physical properties for more commercial applications [9, 10].Transition metals-doped glasses have interesting optical, luminescent, semiconducting, memorizing, and photoconducting properties [11, 12]. Manganese ion is an intriguing transition metal ion although it can be present in a number between valence states (Mn3+ and Mn2+) of different glass matrices [13]. The quantitative characteristics of modifiers and glass formers, size of both ions in the glass structure, field strength, and mobility of the modifier cation, among some other factors, determine the amount of manganese contained in the glass in different forms and valence states [14]. Mn2+ has an electronic configuration of 3d5, which corresponds to a half-filled d shell. The impact of manganese on the thermal, physical, structural, and optical properties of glasses has been the subject of numerous studies [15, 16]. Moreover, manganese ions are well known to have a significant impact on the electric, magnetic, and optical properties of glasses; there seem to be numerous important studies on manganese ions’ environment in different inorganic glass systems available [17].The main objective of this paper is to integrate manganese ions and their impact on structural integrity (namely, different band positions ranges between 487 and 1215 cm−1; optical band gap energy) and insulating character of CdO-Al2O3-P2O5: MnO glasses through a thorough investigation of dielectric constant εl, loss tan δ, and AC conductivity σac within the spectrum of frequency 103 Hz to 105 Hz as well as within the temperature range 20–400°C.


## 2. Experimental Works

Glasses with compositions 39CdO-10Al2O3-(51-x) P2O5: xMnO (0–0.4 mol %) were made using the traditional melt quenching techniques, and the samples were labeled as CAPM_0: 39CdO-10Al2O3-51 P2O5, CAPM_1: 39CdO-10Al2O3-50.9 P2O5: 0.1 MnO, CAPM_2: 39CdO-10Al2O3-50.8 P2O5: 0.2 MnO, CAPM_3: 39CdO-10Al2O3-50.7 P2O5: 0.3 MnO, and CAPM_4: 39CdO-10Al2O3-50.6 P2O5: 0.4 MnO, respectively. Subsequently, the glasses were made using a technique called rapid melt quench, by which the amorphous solid is formed during the melt-quenching process through the gradual toughening (i.e., rise in viscosity) of a melt.In this experiment, the glasses were made using the melt-quenching method. The starting materials CdO, Al2O3, P2O5, and MnO that were used in the making of the present glass systems were of analar grade (greater than 99.9% purity). After polishing, the final glasses’ measurements were 1.0 cm × 1.0 cm × 2.0 cm. For this dielectric analysis, various parameters, namely, dielectric constant δ, dielectric loss tan δ, and AC conductivity δac, were investigated over a broad temperature spectrum and also as a function of wavelength. All these parameters, which were used in this analysis, were measured using LCR Meter (Hewlett-Packard Model-4263B).


## 3. Results and Discussion

### 3.1. Results

From the measured values of densityd, average molecular weight M¯, and refractive index nd of CdO-Al2O3-P2O5: MnO glasses, various other physical parameters, such as manganese ion concentration Ni, mean manganese ion separation Ri,, polaron radius Rp, molar volume VM, electron polarizability αe, reflection loss R, and molar refractivity RM, were calculated and presented in Table 1.Table 1
Different physical characteristics of CdO-Al2O3-P2O5: MnO glasses.
Physical parametersCAPM_0CAPM_1CAPM_2CAPM_3CAPM_4Molecular mass on average,M¯125.481125.418125.368125.351125.312Density,d (g/cm3)5.3515.3605.3625.3715.382Molar volume,VM23.44923.39823.37923.33823.283Refractive index,nd1.5531.5721.6051.6431.692Manganese ion concentration,Ni (×1019 ion/cm3)—0.6721.3452.0172.691Interionic distance,Ri (Å)—1.1410.9050.7910.718Polaron radius,Rp (Å)—0.3520.4440.5090.560Electron polarizability,αe (×10−19 ion/cm3)—0.1170.0610.0430.034Dielectric constant,ε2.4022.4642.5602.6892.856Reflection loss,R0.0460.0490.0530.0580.065Molar refractivity,RM3.6013.7213.8924.0834.332The dopant ion concentration (Ni) could be obtained from(1)Niionscm3=NAMmol %dM¯.The calculated values ofNi, the interionic distance ri and polaron radius rp of dopant ions can be evaluated by the following equations [17]:(2)interionic distanceriA∘=1Ni1/3,polaron radiusriA∘=12π6Ni1/3.Using the refractive index of the glass, the theoretical dielectric constant (ε) was determined:(3)ε=nd2.The Fresnel formula was used to calculate the reflection loss from the glass surface based on the refractive index:(4)R=nd−1nd+12.The following formula was used to calculate the molar refractivityRM for each glass:(5)RM=nd−1nd+2Vm.The following formula was used to measure the molar volume of the glass samples:(6)Vm=M¯d.Using the following formula, the electronic polarizabilityαe was determined:(7)αe=3nd2−14πNind2+2.The number of manganese ions per unit volume is given by the symbolNi.


#### 3.1.1. Differential Thermal Analysis (DTA)

As shown in Figure1, the glass transition temperature Tg, which is between 492 and 523°C, causes an inflection in the spectra and differential thermal analysis (DTA) traces of pure and MnO-doped CdO-Al2O3-P2O5, through which glasses were observed at temperatures ranging from 30 to 1000°C. The crystallization temperature Tc at 698°C to 750°C causes a well-defined exothermic effect, which is accompanied by a well-defined endothermic effect, and melting temperature Tm due to the endothermic effect in the range of 945°C to 956°C. Based on the observed values of Tg, Tc, and Tm, various stability factors of glasses, namely, Tg/Tm, (Tc − Tg)/Tg, and (Tc − Tg)/Tm and the glass forming capacity parameter, which was developed by Hruby, Kg1 = (Tc − Tg)/(Tm − Tc), were calculated and are presented in Table 2.Figure 1
DTA traces of CdO-Al2O3-P2O5: MnO glasses. Inset shows the variation of Tg/Tm, Kg1, (Tc − Tg)/Tg, (Tc − Tg)/Tm, and Tg with MnO concentration.Table 2
Data on DTA analysis of CdO-Al2O3-P2O5: MnO glasses.
GlassesTg (°C)Tc (°C)Tm (°C)Tg/Tm(Tc − Tg)/(Tm − Tc)(Tc − Tg)/Tg(Tc − Tg)/TmCAPM_0493.0698.0945.00.52160.8290.4150.216CAPM_1499.0712.0953.00.52360.8830.4260.223CAPM_2505.5723.0953.00.5300.9450.4300.228CAPM_3511.5732.0954.00.5360.9930.4310.230CAPM_4523.6750.0956.00.5471.0990.4320.236The difference of various stability parameters,Tg/Tm, (Tc − Tg)/Tg, (Tc − Tg)/Tm, and Kg1, with MnO concentration is depicted in the inset of Figure 1. These curves display a growing trend in the stability factors in MnO concentrations increasing from 0.1 wt.% to 0.4 wt.%, implying that the glass network becomes more stable as MnO concentration rises.


#### 3.1.2. IR Studies

Figure2(a) represents the room temperature recordings of pure infrared spectra and manganese oxide-doped CdO-Al2O3-P2O5 glasses. Different IR bands corresponding to phosphate and aluminate structural groups appear in the glass matrix as the concentration of manganese oxide increases. Table 3 shows the data on different band positions from the IR spectra of these glasses.Figure 2
(a) IR spectra of CdO-Al2O3-P2O5: MnO glasses. (b) Variation of symmetrical and asymmetrical band intensities for pure and MnO-doped CdO-Al2O3-P2O5.
(a)(b)Table 3
Data from the infrared spectra of different band positions CdO-Al2O3-P2O5: MnO glasses.
GlassesO-P-O units (cm−1) band 1PO43− units (cm−1) band 2P-O-P units (cm−1) band 3AlO4 units (cm−1)CAPM_01214995896726CAPM_112101005903726CAPM_212071020907726CAPM_312041033911726CAPM_411981047915726For this specific network of glasses, the infrared transmission spectra were recorded for glasses as shown in Figure3, and the conventional bands were caused due to the following:(i)
The O-P-O symmetric stretching vibrations in the range of 1198–1214 cm−1 (band 1)(ii)
The asymmetrical stretching of PO43− groups in the region between 995 cm−1 and 1047 cm−1 (band 2)(iii)
The asymmetrical bending vibrations of P-O-P groups in the range of 896–915 cm−1 (band 3)(iv)
The vibrations of AlO4 groups in the region between 700 cm−1 and 750 cm−1Figure 3
(a) Optical absorption spectra of CdO-Al2O3-P2O5: MnO glasses. (b) Urbach plots of CdO-Al2O3-P2O5: MnO glasses.
(a)(b)The frequency of the band 1 (symmetrical band) changes towards lower frequency as the MnO concentration in the glass matrix increases from 0.1 wt.% to 0.4 wt.%, according to the IR-Spectra. Bands 2 and 3 (symmetrical bands) change towards higher frequency as strength decreases, suggesting a decrease in asymmetric stretching and increase in symmetrical stretching in phosphate units, indicating increased polymerization/stability of the glass network. In the presence of some MnO concentration in the glass network, however, no shift in the band location of AlO4 groups is observed. The difference between symmetrical and asymmetrical band intensities for pure and MnO-doped CdO-Al2O3-P2O5 glasses is depicted in Figure 2(b).


#### 3.1.3. Optical Absorption Studies

Figure3(a) shows the optical absorption spectra of various materials CdO-Al2O3-P2O5: MnO glasses. The spectra of MnO-doped glasses exhibit two absorption bands resulting from Mn2+ transition (around 500 nm) 6A1gS⟶4T1gG and Mn3+ transition (around 490 nm) 5Eg⟶5T2g.There is a change in band positions from 500 to 488 nm as the concentration of MnO rises from 0.1 wt.% to 0.4 wt.%, suggesting the incremental conversion of Mn2+ ions into Mn3+ ions.Figure3(b) presents Urbach plot of CdO-Al2O3-P2O5: MnO glasses. Data on various band positions from the optical absorption spectra are shown in Table 4.Table 4
Data on various band positions from the optical absorption spectra of CdO-Al2O3-P2O5: MnO glasses.
GlassBand edgeλ (nm)Band positionλ (nm) due to Mn2+ transitions 6A1gS⟶4T1gGBand positionλ (nm) due to Mn3+ transition 5Eg⟶5T2gOptical band gap energyEoptUrbach energyΔE (eV)CAPM_0320.5——2.560.61CAPM_1315.7500—2.441.03CAPM_2308.0497.5—2.520.89CAPM_3301.5—4902.530.67CAPM_4300—4882.750.55The optical band gapEopt can be decided based on Urbach plot (αhν)1/2 versus hν, which is related by(8)αv=α0hv−Eopthv2,where α0 is a constant that is proportional to the length of the band tailing and Eopt is the optical band gap energy [12].Finally, MnO concentrations were increased from 0.1 wt.% to 0.4 wt.%.. The observed band positions and measured optical band gaps for these glass series indicate a development in the glass network and an insulating character. A similar trend was also observed from other studies (namely, DTA, IR, and EPR) of CdO-Al2O3-P2O5: MnO glasses.


#### 3.1.4. EPR Studies

Figure4 shows the EPR spectra of CdO-Al2O3-P2O5: at room temperature, MnO glasses were registered. The spectra are characterized by two intense resonance signals; one of them is roughly oriented approximately g = 2.01 (signal 1) with a six-line hyperfine structure that is typical of independent Mn2+ ions, and the other is focusing at g = 4.3 (signal 2), which is a characteristic of isolated Mn3+ ions.Figure 4
EPR spectra of CdO-Al2O3-P2O5: MnO glasses.
(a)(b)(c)(d)As MnO concentration is increased from 0.1 wt.% to 0.4 wt.%, the strength of signal 2 increases at the expense of signal 1, indicating that Mn2+ ions are converted to Mn3+ ions. As the MnO concentration is raised from 0.1 wt.% to 0.4 wt.%, there is a transformation of Mn2+ ions into Mn3+ ions observed in the current glass method, which is an indicative of increased covalent nature over that of ionic.Furthermore, this suggests that the glass polymerization increases with improved stability with MnO concentrations increasing from 0.1 wt.% to 0.4 wt.% in the glass matrix.


#### 3.1.5. Dielectric Studies

Figures5(a)–5(c), respectively, show the variations of dielectric loss tan δ, dielectric constant ε, and AC conductivity δac of CdO-Al2O3-P2O5: MnO glasses with temperature (20°C to 400°C) measured as a function of different frequencies at 1 kHz, 10 kHz, and 100 kHz.Figure 5
(a) Variation of dielectric constant with temperature at different frequencies for CdO-Al2O3-P2O5: MnO glasses. (b) Variation of dielectric loss with temperature at different frequencies for CdO-Al2O3-P2O5: MnO glasses. (c) Variation of AC conductivity with reciprocal temperature at different frequencies for CdO-Al2O3-P2O5: MnO glasses.
(a)(b)(c)Dielectric constantε is observed to increase with temperature (with glass) at any frequency for all glasses; in addition, the value of the dielectric constant decreases as the MnO content rises from 0.1 wt.% to 0.4 wt.%. However, at any given temperature and MnO content in the glass network, it was observed that the dielectric constant reduces as the frequency is increased (Figure 5(a)). A similar trend is observed for dielectric loss tan δ variations (Figure 5(b)).The ac conductivityσac of these glasses is calculated using the following at various temperatures:(9)σ=ωε0εtanδ,where ε0 is the vacuum dielectric constant) for various frequencies.The graph of logσac against 1/T is depicted in Figure 5(c) for all glasses at different frequencies. δac of these glasses is found to increase with temperature and frequency; in addition, it is observed that δac increases with rises in MnO content from 0.1 wt.% to 0.4 wt.% (Figure 3). Similar results were reported for MnO containing various glass matrices [3, 18]. Data on dielectric constant, dielectric loss, and AC conductivity of CdO-Al2O3-P2O5: MnO glasses at 1 kHz, 10 kHz, and 100 kHz for temperatures 20°C and 400°C are presented in Table 5.Table 5
Data on dielectric constant, dielectric loss, and AC conductivity of CdO-Al2O3-P2O5: MnO glasses at 1 kHz, 10 kHz, and 100 kHz for temperatures 20°C and 400°C.
Dielectric constant,ε at 1 kHzDielectric loss, tanδ at 1 kHzAC conductivityσac (×10−9 Ω cm−1) at 1 kHzDielectric constant,ε at 10 kHzDielectric loss, tanδ at 10 kHzAC conductivityσac (×10−9 Ω cm−1) at 10 kHzDielectric constant,ε at 100 kHzDielectric loss, tanδ at 100 kHzAC conductivityσac (×10−9 Ω cm−1) at 100 kHzGlass20°C400°C20°C20°C400°C20°C20°C400°C20°C400°C20°C400°C20°C400°C20°C400°C20°C400°CCAPM_09.9621.920.0020148.4419.80.0015678.4419.80.0015670.0039527.38427.3616.860.000980.0014740.2242CAPM_19.6820.690.001958.1816.650.0015318.1816.650.0015310.0034926.9932.467.1314.230.0009630.0016938.345172.4CAPM_29.3618.860.001877.8814.360.0015077.8814.360.0015070.0030946.62924.86.9512.070.0009480.0019236.78129.7CAPM_39.116.480.001787.6712.640.0014677.6712.640.0014670.0027796.28619.66.7610.540.0009290.0021735.0699.68CAPM_48.7414.680.0009087.3411.260.0014227.3411.260.0014220.0025335.82715.96.549.410.0009080.0025031.144577.38


### 3.2. Discussion

In general, glass properties are determined by its composition and, to a large degree, its structure. Aluminophosphate glasses doped with MnO are a mixture of network formers and modifiers with a complex composition [4, 5, 9, 10, 19]. P2O5 is a well-known network former composed of PO4 structural units, in which one of the four oxygen atoms in the PO4 tetrahedron is doubly bonded to the phosphorous atom [15]. By bridging oxygen atoms, the PO4 tetrahedrons are joined together in chains or rings by covalent bonding. Cross bonds between metal cations and two nonbridging oxygen atoms of each PO4 tetrahedron connect neighboring phosphate chains [14].It is well known that adding a modifier oxide such as CdO to a P2O5 glass matrix causes the conversion of sp2 planar PO3 units to more stable sp3 tetrahedral PO4 units, as well as the formation of nonbridging oxygen atoms [20]. The bands observed at ∼1200 cm−1 and ∼1040 cm−1 result from symmetrical straining vibration (νs(O-P-O)) groups of nonbridging oxygen in phosphate chain and normal vibrational mode of asymmetric straining (vas (PO43−)) group vibrations, respectively [20, 21]. Another band in the vicinity of 895 to 980 cm−1 due to P-O-P bending vibration that corresponds to tendency of asymmetric straining of phosphate group [20] was also observed.Three conventional phosphate bands were visible in the spectra of these lenses due to (i) O-P-O group symmetric straining vibrations in the range 1198–1214 cm−1 (band 1), (ii) PO43− group asymmetrical straining vibrations in the range 995–1047 cm−1 (band 2), and (iii) P-O-P group asymmetrical bending vibrations in the range 896–915 cm−1 (band 3). In addition, a band due to AlO4 group vibrations with a fixed band position at 726 cm−1 was observed for all glasses. From the IR spectral studies of these glasses, it was observed that as the MnO concentration rises from 0.1 wt.% to 0.4 wt.% in the glass matrix, the frequency of the symmetrical band (band 1) of phosphate units shifts towards a reduction in frequency as its intensity increases, and the asymmetrical bands 2 and 3 migrate towards higher frequencies as their intensities decrease, while they shift towards lower frequencies as their intensities decrease. This suggests a reduction in the degree of asymmetric stretching and increase in symmetrical stretching in phosphate units, MnO concentrations were increased from 0.1wt.% to 0.4 wt.%, and there is also a rise in polymerization or stability in the glass network. However, there is no observed change in the band position of AlO4 groups at any concentration of MnO in the glass network.Spectra of optical absorption MnO-doped two distinct absorption bands can be seen in the glasses resulting from Mn2+ transition (around 500 nm) 6A1gS⟶4T1gG and Mn3+ transition (around 490 nm) 5Eg⟶5T2g. The band at 500 nm arises from intraconfigurational transitions due to Mn2+ ions [14, 22]. These detected bands due to Mn2+ ions were hidden, beyond 0.1 wt.% of MnO concentration. Due to the presence of Mn3+ ions, a new strong absorption spectrum with a limit at around 490 nm has emerged [15, 18, 23, 24]. It was observed that the optical band gap increases as the concentration of manganese oxide (MnO) increases from 0.1 wt.% to 0.4 wt.%, whereas the Urbach energy decreases, which indicates improvement in the insulating character and hence the glass network’s strength.Electron spin resonance gives information about the condition of valence of TM ions, local environment, and the essence of their interactions [25]. Since many of those Mn2+ compounds were octahedral and have a top spin structure with five unpaired electrons, they have a top spin arrangement, and an ESR signal with a g value close to the free electron value of 2.0023 is predicted [7, 25]. Signal at g∼2.01 due to Mn2+ ions shows an octahedral symmetrical environment with the bond dominantly ionic [15, 25, 26].In the present study, at room temperature, the EPR spectroscopy of all these glasses was recorded by E11Z Varian X-band (ν=9.5GMZ) ESR Spectrometer. The spectra are characterized by two intense resonance signals; one of them is centered at approximately g = 2.01 (signal 1) with a six-line hyperfine sequence that is typical of independent Mn2+ ions, and the other is centered at g = 4.3 (signal 2), which is a characteristic of isolated Mn3+ ions [26]. The presence of a resonance signal at g = 2.01 is because of the existence of the Mn2+ ion in an area similar to octahedral symmetry. As MnO concentration is increased from 0.1 wt.% to 0.4 wt.%, the strength of signal 2 increases at the cost of signal 1, which is a sign that Mn2+ ions are being converted to Mn3+ ions. These samples’ spectra are identical to those recorded for manganese ions doped in a variety of glass systems [15, 18, 27].Ionic, dipolar, electronic, and space charges all contribute to a material’s dielectric constant. Polarization is determined by the purity and perfection of the lenses [1, 28]. At very low temperatures, the effect of space charge polarizations is negligible, but it is within the low frequency range, and there is a significant difference [28]. The dipolar alignment effects in the glasses can be observed at up to 106 Hz. Retrieving our information, we find that ε is slightly frequency-dependent even at room temperature for pure as well as MnO-doped glasses. This is because of the dielectric constant and loss being influenced by space charge polarization. For temperature changes of around 400°C, for many solids, the reduction within the electronic dielectric constant is found to be less than 3% [29]. The defects in glasses can only increase ε and tanδ. As the temperature rises, space charge polarization becomes more dominant and therefore increases [1, 28, 29]. As this form of polarization decreases with frequency, the change in ε and tan δ at higher frequencies and temperature is lower [30–38].The values increased by up to 0.5% with the addition of MnO, andtanδ, σac, and ε are found to decrease at any temperature and frequency. Modifiers, such as octahedral Mn2+ ion, weaken the glass network by creating paths for free ions to migrate through, accumulating space charge and increasing disorder. The space charge polarization increases as the glass network becomes weaker, resulting in a reduction in dielectric parameters (i.e., MnO concentration ranging from 0.1 to 0.4). In MnO-doped glasses, the decrease of these parameters in this concentration range suggests that the Mn3+ ions present in these glasses (as demonstrated by measurements of optical absorption) establish cross-linkages, where Al-O-Mn bonds are formed by combining a portion of AlO3 unit ions with a portion of AlO3 unit ions. This is also logical because Al3+ and the oxidation state of Mn3+ ions are nearly identical, and their ionic radii are nearly similar (0.51 Å and 0.66 Å, respectively). As a result of these cross-links, the space charge polarization of glasses with MnO concentrations decreases, resulting in lower dielectric parameter values. As a result of increased concentration of MnO in the lenses, the existence of the tan variation often supports that the bulks of the magnesium oxide in the glasses CAPM_1 and CAPM_2 are in the Mn2+ state, which acts as modifiers, and in the glasses CAPM_3 and CAPM_4, they are in the Mn3+ state, which act as formers.


## 3.1. Results

From the measured values of densityd, average molecular weight M¯, and refractive index nd of CdO-Al2O3-P2O5: MnO glasses, various other physical parameters, such as manganese ion concentration Ni, mean manganese ion separation Ri,, polaron radius Rp, molar volume VM, electron polarizability αe, reflection loss R, and molar refractivity RM, were calculated and presented in Table 1.Table 1
Different physical characteristics of CdO-Al2O3-P2O5: MnO glasses.
Physical parametersCAPM_0CAPM_1CAPM_2CAPM_3CAPM_4Molecular mass on average,M¯125.481125.418125.368125.351125.312Density,d (g/cm3)5.3515.3605.3625.3715.382Molar volume,VM23.44923.39823.37923.33823.283Refractive index,nd1.5531.5721.6051.6431.692Manganese ion concentration,Ni (×1019 ion/cm3)—0.6721.3452.0172.691Interionic distance,Ri (Å)—1.1410.9050.7910.718Polaron radius,Rp (Å)—0.3520.4440.5090.560Electron polarizability,αe (×10−19 ion/cm3)—0.1170.0610.0430.034Dielectric constant,ε2.4022.4642.5602.6892.856Reflection loss,R0.0460.0490.0530.0580.065Molar refractivity,RM3.6013.7213.8924.0834.332The dopant ion concentration (Ni) could be obtained from(1)Niionscm3=NAMmol %dM¯.The calculated values ofNi, the interionic distance ri and polaron radius rp of dopant ions can be evaluated by the following equations [17]:(2)interionic distanceriA∘=1Ni1/3,polaron radiusriA∘=12π6Ni1/3.Using the refractive index of the glass, the theoretical dielectric constant (ε) was determined:(3)ε=nd2.The Fresnel formula was used to calculate the reflection loss from the glass surface based on the refractive index:(4)R=nd−1nd+12.The following formula was used to calculate the molar refractivityRM for each glass:(5)RM=nd−1nd+2Vm.The following formula was used to measure the molar volume of the glass samples:(6)Vm=M¯d.Using the following formula, the electronic polarizabilityαe was determined:(7)αe=3nd2−14πNind2+2.The number of manganese ions per unit volume is given by the symbolNi.


### 3.1.1. Differential Thermal Analysis (DTA)

As shown in Figure1, the glass transition temperature Tg, which is between 492 and 523°C, causes an inflection in the spectra and differential thermal analysis (DTA) traces of pure and MnO-doped CdO-Al2O3-P2O5, through which glasses were observed at temperatures ranging from 30 to 1000°C. The crystallization temperature Tc at 698°C to 750°C causes a well-defined exothermic effect, which is accompanied by a well-defined endothermic effect, and melting temperature Tm due to the endothermic effect in the range of 945°C to 956°C. Based on the observed values of Tg, Tc, and Tm, various stability factors of glasses, namely, Tg/Tm, (Tc − Tg)/Tg, and (Tc − Tg)/Tm and the glass forming capacity parameter, which was developed by Hruby, Kg1 = (Tc − Tg)/(Tm − Tc), were calculated and are presented in Table 2.Figure 1
DTA traces of CdO-Al2O3-P2O5: MnO glasses. Inset shows the variation of Tg/Tm, Kg1, (Tc − Tg)/Tg, (Tc − Tg)/Tm, and Tg with MnO concentration.Table 2
Data on DTA analysis of CdO-Al2O3-P2O5: MnO glasses.
GlassesTg (°C)Tc (°C)Tm (°C)Tg/Tm(Tc − Tg)/(Tm − Tc)(Tc − Tg)/Tg(Tc − Tg)/TmCAPM_0493.0698.0945.00.52160.8290.4150.216CAPM_1499.0712.0953.00.52360.8830.4260.223CAPM_2505.5723.0953.00.5300.9450.4300.228CAPM_3511.5732.0954.00.5360.9930.4310.230CAPM_4523.6750.0956.00.5471.0990.4320.236The difference of various stability parameters,Tg/Tm, (Tc − Tg)/Tg, (Tc − Tg)/Tm, and Kg1, with MnO concentration is depicted in the inset of Figure 1. These curves display a growing trend in the stability factors in MnO concentrations increasing from 0.1 wt.% to 0.4 wt.%, implying that the glass network becomes more stable as MnO concentration rises.


### 3.1.2. IR Studies

Figure2(a) represents the room temperature recordings of pure infrared spectra and manganese oxide-doped CdO-Al2O3-P2O5 glasses. Different IR bands corresponding to phosphate and aluminate structural groups appear in the glass matrix as the concentration of manganese oxide increases. Table 3 shows the data on different band positions from the IR spectra of these glasses.Figure 2
(a) IR spectra of CdO-Al2O3-P2O5: MnO glasses. (b) Variation of symmetrical and asymmetrical band intensities for pure and MnO-doped CdO-Al2O3-P2O5.
(a)(b)Table 3
Data from the infrared spectra of different band positions CdO-Al2O3-P2O5: MnO glasses.
GlassesO-P-O units (cm−1) band 1PO43− units (cm−1) band 2P-O-P units (cm−1) band 3AlO4 units (cm−1)CAPM_01214995896726CAPM_112101005903726CAPM_212071020907726CAPM_312041033911726CAPM_411981047915726For this specific network of glasses, the infrared transmission spectra were recorded for glasses as shown in Figure3, and the conventional bands were caused due to the following:(i)
The O-P-O symmetric stretching vibrations in the range of 1198–1214 cm−1 (band 1)(ii)
The asymmetrical stretching of PO43− groups in the region between 995 cm−1 and 1047 cm−1 (band 2)(iii)
The asymmetrical bending vibrations of P-O-P groups in the range of 896–915 cm−1 (band 3)(iv)
The vibrations of AlO4 groups in the region between 700 cm−1 and 750 cm−1Figure 3
(a) Optical absorption spectra of CdO-Al2O3-P2O5: MnO glasses. (b) Urbach plots of CdO-Al2O3-P2O5: MnO glasses.
(a)(b)The frequency of the band 1 (symmetrical band) changes towards lower frequency as the MnO concentration in the glass matrix increases from 0.1 wt.% to 0.4 wt.%, according to the IR-Spectra. Bands 2 and 3 (symmetrical bands) change towards higher frequency as strength decreases, suggesting a decrease in asymmetric stretching and increase in symmetrical stretching in phosphate units, indicating increased polymerization/stability of the glass network. In the presence of some MnO concentration in the glass network, however, no shift in the band location of AlO4 groups is observed. The difference between symmetrical and asymmetrical band intensities for pure and MnO-doped CdO-Al2O3-P2O5 glasses is depicted in Figure 2(b).


### 3.1.3. Optical Absorption Studies

Figure3(a) shows the optical absorption spectra of various materials CdO-Al2O3-P2O5: MnO glasses. The spectra of MnO-doped glasses exhibit two absorption bands resulting from Mn2+ transition (around 500 nm) 6A1gS⟶4T1gG and Mn3+ transition (around 490 nm) 5Eg⟶5T2g.There is a change in band positions from 500 to 488 nm as the concentration of MnO rises from 0.1 wt.% to 0.4 wt.%, suggesting the incremental conversion of Mn2+ ions into Mn3+ ions.Figure3(b) presents Urbach plot of CdO-Al2O3-P2O5: MnO glasses. Data on various band positions from the optical absorption spectra are shown in Table 4.Table 4
Data on various band positions from the optical absorption spectra of CdO-Al2O3-P2O5: MnO glasses.
GlassBand edgeλ (nm)Band positionλ (nm) due to Mn2+ transitions 6A1gS⟶4T1gGBand positionλ (nm) due to Mn3+ transition 5Eg⟶5T2gOptical band gap energyEoptUrbach energyΔE (eV)CAPM_0320.5——2.560.61CAPM_1315.7500—2.441.03CAPM_2308.0497.5—2.520.89CAPM_3301.5—4902.530.67CAPM_4300—4882.750.55The optical band gapEopt can be decided based on Urbach plot (αhν)1/2 versus hν, which is related by(8)αv=α0hv−Eopthv2,where α0 is a constant that is proportional to the length of the band tailing and Eopt is the optical band gap energy [12].Finally, MnO concentrations were increased from 0.1 wt.% to 0.4 wt.%.. The observed band positions and measured optical band gaps for these glass series indicate a development in the glass network and an insulating character. A similar trend was also observed from other studies (namely, DTA, IR, and EPR) of CdO-Al2O3-P2O5: MnO glasses.


### 3.1.4. EPR Studies

Figure4 shows the EPR spectra of CdO-Al2O3-P2O5: at room temperature, MnO glasses were registered. The spectra are characterized by two intense resonance signals; one of them is roughly oriented approximately g = 2.01 (signal 1) with a six-line hyperfine structure that is typical of independent Mn2+ ions, and the other is focusing at g = 4.3 (signal 2), which is a characteristic of isolated Mn3+ ions.Figure 4
EPR spectra of CdO-Al2O3-P2O5: MnO glasses.
(a)(b)(c)(d)As MnO concentration is increased from 0.1 wt.% to 0.4 wt.%, the strength of signal 2 increases at the expense of signal 1, indicating that Mn2+ ions are converted to Mn3+ ions. As the MnO concentration is raised from 0.1 wt.% to 0.4 wt.%, there is a transformation of Mn2+ ions into Mn3+ ions observed in the current glass method, which is an indicative of increased covalent nature over that of ionic.Furthermore, this suggests that the glass polymerization increases with improved stability with MnO concentrations increasing from 0.1 wt.% to 0.4 wt.% in the glass matrix.


### 3.1.5. Dielectric Studies

Figures5(a)–5(c), respectively, show the variations of dielectric loss tan δ, dielectric constant ε, and AC conductivity δac of CdO-Al2O3-P2O5: MnO glasses with temperature (20°C to 400°C) measured as a function of different frequencies at 1 kHz, 10 kHz, and 100 kHz.Figure 5
(a) Variation of dielectric constant with temperature at different frequencies for CdO-Al2O3-P2O5: MnO glasses. (b) Variation of dielectric loss with temperature at different frequencies for CdO-Al2O3-P2O5: MnO glasses. (c) Variation of AC conductivity with reciprocal temperature at different frequencies for CdO-Al2O3-P2O5: MnO glasses.
(a)(b)(c)Dielectric constantε is observed to increase with temperature (with glass) at any frequency for all glasses; in addition, the value of the dielectric constant decreases as the MnO content rises from 0.1 wt.% to 0.4 wt.%. However, at any given temperature and MnO content in the glass network, it was observed that the dielectric constant reduces as the frequency is increased (Figure 5(a)). A similar trend is observed for dielectric loss tan δ variations (Figure 5(b)).The ac conductivityσac of these glasses is calculated using the following at various temperatures:(9)σ=ωε0εtanδ,where ε0 is the vacuum dielectric constant) for various frequencies.The graph of logσac against 1/T is depicted in Figure 5(c) for all glasses at different frequencies. δac of these glasses is found to increase with temperature and frequency; in addition, it is observed that δac increases with rises in MnO content from 0.1 wt.% to 0.4 wt.% (Figure 3). Similar results were reported for MnO containing various glass matrices [3, 18]. Data on dielectric constant, dielectric loss, and AC conductivity of CdO-Al2O3-P2O5: MnO glasses at 1 kHz, 10 kHz, and 100 kHz for temperatures 20°C and 400°C are presented in Table 5.Table 5
Data on dielectric constant, dielectric loss, and AC conductivity of CdO-Al2O3-P2O5: MnO glasses at 1 kHz, 10 kHz, and 100 kHz for temperatures 20°C and 400°C.
Dielectric constant,ε at 1 kHzDielectric loss, tanδ at 1 kHzAC conductivityσac (×10−9 Ω cm−1) at 1 kHzDielectric constant,ε at 10 kHzDielectric loss, tanδ at 10 kHzAC conductivityσac (×10−9 Ω cm−1) at 10 kHzDielectric constant,ε at 100 kHzDielectric loss, tanδ at 100 kHzAC conductivityσac (×10−9 Ω cm−1) at 100 kHzGlass20°C400°C20°C20°C400°C20°C20°C400°C20°C400°C20°C400°C20°C400°C20°C400°C20°C400°CCAPM_09.9621.920.0020148.4419.80.0015678.4419.80.0015670.0039527.38427.3616.860.000980.0014740.2242CAPM_19.6820.690.001958.1816.650.0015318.1816.650.0015310.0034926.9932.467.1314.230.0009630.0016938.345172.4CAPM_29.3618.860.001877.8814.360.0015077.8814.360.0015070.0030946.62924.86.9512.070.0009480.0019236.78129.7CAPM_39.116.480.001787.6712.640.0014677.6712.640.0014670.0027796.28619.66.7610.540.0009290.0021735.0699.68CAPM_48.7414.680.0009087.3411.260.0014227.3411.260.0014220.0025335.82715.96.549.410.0009080.0025031.144577.38


## 3.1.1. Differential Thermal Analysis (DTA)

As shown in Figure1, the glass transition temperature Tg, which is between 492 and 523°C, causes an inflection in the spectra and differential thermal analysis (DTA) traces of pure and MnO-doped CdO-Al2O3-P2O5, through which glasses were observed at temperatures ranging from 30 to 1000°C. The crystallization temperature Tc at 698°C to 750°C causes a well-defined exothermic effect, which is accompanied by a well-defined endothermic effect, and melting temperature Tm due to the endothermic effect in the range of 945°C to 956°C. Based on the observed values of Tg, Tc, and Tm, various stability factors of glasses, namely, Tg/Tm, (Tc − Tg)/Tg, and (Tc − Tg)/Tm and the glass forming capacity parameter, which was developed by Hruby, Kg1 = (Tc − Tg)/(Tm − Tc), were calculated and are presented in Table 2.Figure 1
DTA traces of CdO-Al2O3-P2O5: MnO glasses. Inset shows the variation of Tg/Tm, Kg1, (Tc − Tg)/Tg, (Tc − Tg)/Tm, and Tg with MnO concentration.Table 2
Data on DTA analysis of CdO-Al2O3-P2O5: MnO glasses.
GlassesTg (°C)Tc (°C)Tm (°C)Tg/Tm(Tc − Tg)/(Tm − Tc)(Tc − Tg)/Tg(Tc − Tg)/TmCAPM_0493.0698.0945.00.52160.8290.4150.216CAPM_1499.0712.0953.00.52360.8830.4260.223CAPM_2505.5723.0953.00.5300.9450.4300.228CAPM_3511.5732.0954.00.5360.9930.4310.230CAPM_4523.6750.0956.00.5471.0990.4320.236The difference of various stability parameters,Tg/Tm, (Tc − Tg)/Tg, (Tc − Tg)/Tm, and Kg1, with MnO concentration is depicted in the inset of Figure 1. These curves display a growing trend in the stability factors in MnO concentrations increasing from 0.1 wt.% to 0.4 wt.%, implying that the glass network becomes more stable as MnO concentration rises.


## 3.1.2. IR Studies

Figure2(a) represents the room temperature recordings of pure infrared spectra and manganese oxide-doped CdO-Al2O3-P2O5 glasses. Different IR bands corresponding to phosphate and aluminate structural groups appear in the glass matrix as the concentration of manganese oxide increases. Table 3 shows the data on different band positions from the IR spectra of these glasses.Figure 2
(a) IR spectra of CdO-Al2O3-P2O5: MnO glasses. (b) Variation of symmetrical and asymmetrical band intensities for pure and MnO-doped CdO-Al2O3-P2O5.
(a)(b)Table 3
Data from the infrared spectra of different band positions CdO-Al2O3-P2O5: MnO glasses.
GlassesO-P-O units (cm−1) band 1PO43− units (cm−1) band 2P-O-P units (cm−1) band 3AlO4 units (cm−1)CAPM_01214995896726CAPM_112101005903726CAPM_212071020907726CAPM_312041033911726CAPM_411981047915726For this specific network of glasses, the infrared transmission spectra were recorded for glasses as shown in Figure3, and the conventional bands were caused due to the following:(i)
The O-P-O symmetric stretching vibrations in the range of 1198–1214 cm−1 (band 1)(ii)
The asymmetrical stretching of PO43− groups in the region between 995 cm−1 and 1047 cm−1 (band 2)(iii)
The asymmetrical bending vibrations of P-O-P groups in the range of 896–915 cm−1 (band 3)(iv)
The vibrations of AlO4 groups in the region between 700 cm−1 and 750 cm−1Figure 3
(a) Optical absorption spectra of CdO-Al2O3-P2O5: MnO glasses. (b) Urbach plots of CdO-Al2O3-P2O5: MnO glasses.
(a)(b)The frequency of the band 1 (symmetrical band) changes towards lower frequency as the MnO concentration in the glass matrix increases from 0.1 wt.% to 0.4 wt.%, according to the IR-Spectra. Bands 2 and 3 (symmetrical bands) change towards higher frequency as strength decreases, suggesting a decrease in asymmetric stretching and increase in symmetrical stretching in phosphate units, indicating increased polymerization/stability of the glass network. In the presence of some MnO concentration in the glass network, however, no shift in the band location of AlO4 groups is observed. The difference between symmetrical and asymmetrical band intensities for pure and MnO-doped CdO-Al2O3-P2O5 glasses is depicted in Figure 2(b).


## 3.1.3. Optical Absorption Studies

Figure3(a) shows the optical absorption spectra of various materials CdO-Al2O3-P2O5: MnO glasses. The spectra of MnO-doped glasses exhibit two absorption bands resulting from Mn2+ transition (around 500 nm) 6A1gS⟶4T1gG and Mn3+ transition (around 490 nm) 5Eg⟶5T2g.There is a change in band positions from 500 to 488 nm as the concentration of MnO rises from 0.1 wt.% to 0.4 wt.%, suggesting the incremental conversion of Mn2+ ions into Mn3+ ions.Figure3(b) presents Urbach plot of CdO-Al2O3-P2O5: MnO glasses. Data on various band positions from the optical absorption spectra are shown in Table 4.Table 4
Data on various band positions from the optical absorption spectra of CdO-Al2O3-P2O5: MnO glasses.
GlassBand edgeλ (nm)Band positionλ (nm) due to Mn2+ transitions 6A1gS⟶4T1gGBand positionλ (nm) due to Mn3+ transition 5Eg⟶5T2gOptical band gap energyEoptUrbach energyΔE (eV)CAPM_0320.5——2.560.61CAPM_1315.7500—2.441.03CAPM_2308.0497.5—2.520.89CAPM_3301.5—4902.530.67CAPM_4300—4882.750.55The optical band gapEopt can be decided based on Urbach plot (αhν)1/2 versus hν, which is related by(8)αv=α0hv−Eopthv2,where α0 is a constant that is proportional to the length of the band tailing and Eopt is the optical band gap energy [12].Finally, MnO concentrations were increased from 0.1 wt.% to 0.4 wt.%.. The observed band positions and measured optical band gaps for these glass series indicate a development in the glass network and an insulating character. A similar trend was also observed from other studies (namely, DTA, IR, and EPR) of CdO-Al2O3-P2O5: MnO glasses.


## 3.1.4. EPR Studies

Figure4 shows the EPR spectra of CdO-Al2O3-P2O5: at room temperature, MnO glasses were registered. The spectra are characterized by two intense resonance signals; one of them is roughly oriented approximately g = 2.01 (signal 1) with a six-line hyperfine structure that is typical of independent Mn2+ ions, and the other is focusing at g = 4.3 (signal 2), which is a characteristic of isolated Mn3+ ions.Figure 4
EPR spectra of CdO-Al2O3-P2O5: MnO glasses.
(a)(b)(c)(d)As MnO concentration is increased from 0.1 wt.% to 0.4 wt.%, the strength of signal 2 increases at the expense of signal 1, indicating that Mn2+ ions are converted to Mn3+ ions. As the MnO concentration is raised from 0.1 wt.% to 0.4 wt.%, there is a transformation of Mn2+ ions into Mn3+ ions observed in the current glass method, which is an indicative of increased covalent nature over that of ionic.Furthermore, this suggests that the glass polymerization increases with improved stability with MnO concentrations increasing from 0.1 wt.% to 0.4 wt.% in the glass matrix.


## 3.1.5. Dielectric Studies

Figures5(a)–5(c), respectively, show the variations of dielectric loss tan δ, dielectric constant ε, and AC conductivity δac of CdO-Al2O3-P2O5: MnO glasses with temperature (20°C to 400°C) measured as a function of different frequencies at 1 kHz, 10 kHz, and 100 kHz.Figure 5
(a) Variation of dielectric constant with temperature at different frequencies for CdO-Al2O3-P2O5: MnO glasses. (b) Variation of dielectric loss with temperature at different frequencies for CdO-Al2O3-P2O5: MnO glasses. (c) Variation of AC conductivity with reciprocal temperature at different frequencies for CdO-Al2O3-P2O5: MnO glasses.
(a)(b)(c)Dielectric constantε is observed to increase with temperature (with glass) at any frequency for all glasses; in addition, the value of the dielectric constant decreases as the MnO content rises from 0.1 wt.% to 0.4 wt.%. However, at any given temperature and MnO content in the glass network, it was observed that the dielectric constant reduces as the frequency is increased (Figure 5(a)). A similar trend is observed for dielectric loss tan δ variations (Figure 5(b)).The ac conductivityσac of these glasses is calculated using the following at various temperatures:(9)σ=ωε0εtanδ,where ε0 is the vacuum dielectric constant) for various frequencies.The graph of logσac against 1/T is depicted in Figure 5(c) for all glasses at different frequencies. δac of these glasses is found to increase with temperature and frequency; in addition, it is observed that δac increases with rises in MnO content from 0.1 wt.% to 0.4 wt.% (Figure 3). Similar results were reported for MnO containing various glass matrices [3, 18]. Data on dielectric constant, dielectric loss, and AC conductivity of CdO-Al2O3-P2O5: MnO glasses at 1 kHz, 10 kHz, and 100 kHz for temperatures 20°C and 400°C are presented in Table 5.Table 5
Data on dielectric constant, dielectric loss, and AC conductivity of CdO-Al2O3-P2O5: MnO glasses at 1 kHz, 10 kHz, and 100 kHz for temperatures 20°C and 400°C.
Dielectric constant,ε at 1 kHzDielectric loss, tanδ at 1 kHzAC conductivityσac (×10−9 Ω cm−1) at 1 kHzDielectric constant,ε at 10 kHzDielectric loss, tanδ at 10 kHzAC conductivityσac (×10−9 Ω cm−1) at 10 kHzDielectric constant,ε at 100 kHzDielectric loss, tanδ at 100 kHzAC conductivityσac (×10−9 Ω cm−1) at 100 kHzGlass20°C400°C20°C20°C400°C20°C20°C400°C20°C400°C20°C400°C20°C400°C20°C400°C20°C400°CCAPM_09.9621.920.0020148.4419.80.0015678.4419.80.0015670.0039527.38427.3616.860.000980.0014740.2242CAPM_19.6820.690.001958.1816.650.0015318.1816.650.0015310.0034926.9932.467.1314.230.0009630.0016938.345172.4CAPM_29.3618.860.001877.8814.360.0015077.8814.360.0015070.0030946.62924.86.9512.070.0009480.0019236.78129.7CAPM_39.116.480.001787.6712.640.0014677.6712.640.0014670.0027796.28619.66.7610.540.0009290.0021735.0699.68CAPM_48.7414.680.0009087.3411.260.0014227.3411.260.0014220.0025335.82715.96.549.410.0009080.0025031.144577.38


## 3.2. Discussion

In general, glass properties are determined by its composition and, to a large degree, its structure. Aluminophosphate glasses doped with MnO are a mixture of network formers and modifiers with a complex composition [4, 5, 9, 10, 19]. P2O5 is a well-known network former composed of PO4 structural units, in which one of the four oxygen atoms in the PO4 tetrahedron is doubly bonded to the phosphorous atom [15]. By bridging oxygen atoms, the PO4 tetrahedrons are joined together in chains or rings by covalent bonding. Cross bonds between metal cations and two nonbridging oxygen atoms of each PO4 tetrahedron connect neighboring phosphate chains [14].It is well known that adding a modifier oxide such as CdO to a P2O5 glass matrix causes the conversion of sp2 planar PO3 units to more stable sp3 tetrahedral PO4 units, as well as the formation of nonbridging oxygen atoms [20]. The bands observed at ∼1200 cm−1 and ∼1040 cm−1 result from symmetrical straining vibration (νs(O-P-O)) groups of nonbridging oxygen in phosphate chain and normal vibrational mode of asymmetric straining (vas (PO43−)) group vibrations, respectively [20, 21]. Another band in the vicinity of 895 to 980 cm−1 due to P-O-P bending vibration that corresponds to tendency of asymmetric straining of phosphate group [20] was also observed.Three conventional phosphate bands were visible in the spectra of these lenses due to (i) O-P-O group symmetric straining vibrations in the range 1198–1214 cm−1 (band 1), (ii) PO43− group asymmetrical straining vibrations in the range 995–1047 cm−1 (band 2), and (iii) P-O-P group asymmetrical bending vibrations in the range 896–915 cm−1 (band 3). In addition, a band due to AlO4 group vibrations with a fixed band position at 726 cm−1 was observed for all glasses. From the IR spectral studies of these glasses, it was observed that as the MnO concentration rises from 0.1 wt.% to 0.4 wt.% in the glass matrix, the frequency of the symmetrical band (band 1) of phosphate units shifts towards a reduction in frequency as its intensity increases, and the asymmetrical bands 2 and 3 migrate towards higher frequencies as their intensities decrease, while they shift towards lower frequencies as their intensities decrease. This suggests a reduction in the degree of asymmetric stretching and increase in symmetrical stretching in phosphate units, MnO concentrations were increased from 0.1wt.% to 0.4 wt.%, and there is also a rise in polymerization or stability in the glass network. However, there is no observed change in the band position of AlO4 groups at any concentration of MnO in the glass network.Spectra of optical absorption MnO-doped two distinct absorption bands can be seen in the glasses resulting from Mn2+ transition (around 500 nm) 6A1gS⟶4T1gG and Mn3+ transition (around 490 nm) 5Eg⟶5T2g. The band at 500 nm arises from intraconfigurational transitions due to Mn2+ ions [14, 22]. These detected bands due to Mn2+ ions were hidden, beyond 0.1 wt.% of MnO concentration. Due to the presence of Mn3+ ions, a new strong absorption spectrum with a limit at around 490 nm has emerged [15, 18, 23, 24]. It was observed that the optical band gap increases as the concentration of manganese oxide (MnO) increases from 0.1 wt.% to 0.4 wt.%, whereas the Urbach energy decreases, which indicates improvement in the insulating character and hence the glass network’s strength.Electron spin resonance gives information about the condition of valence of TM ions, local environment, and the essence of their interactions [25]. Since many of those Mn2+ compounds were octahedral and have a top spin structure with five unpaired electrons, they have a top spin arrangement, and an ESR signal with a g value close to the free electron value of 2.0023 is predicted [7, 25]. Signal at g∼2.01 due to Mn2+ ions shows an octahedral symmetrical environment with the bond dominantly ionic [15, 25, 26].In the present study, at room temperature, the EPR spectroscopy of all these glasses was recorded by E11Z Varian X-band (ν=9.5GMZ) ESR Spectrometer. The spectra are characterized by two intense resonance signals; one of them is centered at approximately g = 2.01 (signal 1) with a six-line hyperfine sequence that is typical of independent Mn2+ ions, and the other is centered at g = 4.3 (signal 2), which is a characteristic of isolated Mn3+ ions [26]. The presence of a resonance signal at g = 2.01 is because of the existence of the Mn2+ ion in an area similar to octahedral symmetry. As MnO concentration is increased from 0.1 wt.% to 0.4 wt.%, the strength of signal 2 increases at the cost of signal 1, which is a sign that Mn2+ ions are being converted to Mn3+ ions. These samples’ spectra are identical to those recorded for manganese ions doped in a variety of glass systems [15, 18, 27].Ionic, dipolar, electronic, and space charges all contribute to a material’s dielectric constant. Polarization is determined by the purity and perfection of the lenses [1, 28]. At very low temperatures, the effect of space charge polarizations is negligible, but it is within the low frequency range, and there is a significant difference [28]. The dipolar alignment effects in the glasses can be observed at up to 106 Hz. Retrieving our information, we find that ε is slightly frequency-dependent even at room temperature for pure as well as MnO-doped glasses. This is because of the dielectric constant and loss being influenced by space charge polarization. For temperature changes of around 400°C, for many solids, the reduction within the electronic dielectric constant is found to be less than 3% [29]. The defects in glasses can only increase ε and tanδ. As the temperature rises, space charge polarization becomes more dominant and therefore increases [1, 28, 29]. As this form of polarization decreases with frequency, the change in ε and tan δ at higher frequencies and temperature is lower [30–38].The values increased by up to 0.5% with the addition of MnO, andtanδ, σac, and ε are found to decrease at any temperature and frequency. Modifiers, such as octahedral Mn2+ ion, weaken the glass network by creating paths for free ions to migrate through, accumulating space charge and increasing disorder. The space charge polarization increases as the glass network becomes weaker, resulting in a reduction in dielectric parameters (i.e., MnO concentration ranging from 0.1 to 0.4). In MnO-doped glasses, the decrease of these parameters in this concentration range suggests that the Mn3+ ions present in these glasses (as demonstrated by measurements of optical absorption) establish cross-linkages, where Al-O-Mn bonds are formed by combining a portion of AlO3 unit ions with a portion of AlO3 unit ions. This is also logical because Al3+ and the oxidation state of Mn3+ ions are nearly identical, and their ionic radii are nearly similar (0.51 Å and 0.66 Å, respectively). As a result of these cross-links, the space charge polarization of glasses with MnO concentrations decreases, resulting in lower dielectric parameter values. As a result of increased concentration of MnO in the lenses, the existence of the tan variation often supports that the bulks of the magnesium oxide in the glasses CAPM_1 and CAPM_2 are in the Mn2+ state, which acts as modifiers, and in the glasses CAPM_3 and CAPM_4, they are in the Mn3+ state, which act as formers.


## 4. Conclusion

The conclusions drawn from different physical studies and spectroscopic properties of CdO-Al2O3-P2O5: MnO glasses are summarized as follows.(i)
The increase of MnO content from 0.1 wt.% to 0.4 wt.% improved glass network stability in the temperature range of 30–1000°C, according to DTA traces registered in the temperature range of 30–1000°C.(ii)
With the improvement due to MnO content increase from 0.1 wt.% to 0.4 wt.%, the IR spectra measured at room temperature showed a rise in the symmetrical bands’ intensity (band 1) at the expense of asymmetrical bands (bands 2 and 3); the observed trend indicates that the glass network’s stability has improved.(iii)
The gradual transformation of Mn2+ ions into Mn3+ by increasing MnO concentrations from 0.1 wt.% to 0.4 wt.% was observed in EPR spectra measured at room temperature, indicating an enhanced covalent atmosphere of manganese ions as well as an improvement in the consistency of the glass network.(iv)
The MnO production was increased from 0.1 wt.% to 0.4 wt.% with an improvement in MnO content percent, and optical absorption spectra showed a shift in the concentration of Mn3+ ions at the cost of Mn2+ ions, as well as a rise throughout the optical band gap; the observed pattern shows an increase in insulating character and thereby the stability of the glass network.(v)
At 105 Hz, the dielectric constant of glassM0 (pure glass) is determined to be 7.36 at room temperature and it was frequency-oriented, with lower frequencies having comparatively higher values. With an improvement in MnO concentration of up to 0.4 wt.%, the dielectric constant value decreases with introduction of MnO. The variance of dielectric loss of frequency at different temperatures reveals a consistent pattern across all glasses.(vi)
The space charge polarization increases as the glass network becomes weaker, resulting in higher measures of dielectric parameters. As more Mn3+ is added to the network of glasses, the space charge polarization decreases, resulting in a decrease in the measures of the dielectric parameters of the glasses.(vii)
For all types of glasses at different frequencies,δac of these glasses is found to increase with temperature and frequency; in addition, it is observed that as δac decreases, MnO content was increased from 0.1 wt.% to 0.4 wt.%. This indicates that high proportion of Mn2+ in glass CAPM_1 (taking modiﬁer positions) and high proportion of Mn3+ in glass CAPM_4 (when glass former position high insulating character was considered).(viii)
Finally, the results from various studies made on CdO-Al2O3-P2O5: MnO glasses reveal an improved stability of the glass network with increase in MnO content from 0.1 wt.% to 0.4 wt.%.



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*Source: 6253069-2021-06-29.xml*