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# Structural and Dielectric Properties of Mg(1-x)CaxTiO3 (x=0.7, 0.8) Ceramic Materials

V Sharon Samyuktha, T Subba Rao, R Padma Suvarna

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V Sharon Samyuktha, T Subba Rao, R Padma Suvarna. Structural and Dielectric Properties of Mg(1-x)CaxTiO3 (x=0.7, 0.8) Ceramic Materials. Mechanics, Materials Science & Engineering Journal, 2017, 8, 10.2412/mmse.30.345.847. hal-01500636

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Distributed under a Creative Commons Attribution 4.0 International License
Structural and Dielectric Properties of Mg(1-x)CaxTiO3 (x=0.7, 0.8) Ceramic Materials

V. Sharon Samyuktha ¹, T. Subba Rao ², R. Padma Suvarna¹

1 – JNTUA, Anantapuram, Andhra Pradesh, India-515001

2 – Sri Krishna Devaraya University, Andhra Pradesh, India-515003

<figure><img src="image_3.png" /></figure>

DOI 10.2412/mmse.30.345.847 provided by [Seo4U.link](http://Seo4U.link)

**Keywords:** calcium magnesium titanate, solid state reaction method, dielectric response, XRD.

**ABSTRACT.** Calcium Magnesium titanate ceramic materials with the molar formula $Mg_{(1-x)}Ca_xTiO_3$ in which the x varies from 0.7 to 0.8 were synthesized by conventional Solid State Reaction method. The XRD pattern revealed that the samples exhibit Orthorhombic structure. The microstructure and surface morphology for the samples was studied by SEM. The elemental composition was studied by EDAX. The dielectric response of both samples was measured by HIOKI 3532-50 LCR HiTESTER in the frequency range of 1KHz-1MHz from room temperature to 350°C. These samples find applications in capacitors, microwave antennas, stainless steel electrodes and data storage devices.

**Introduction.** Over more than 200 years, Ceramic materials are known for technical applications. To overcome the limitations of other conventional materials, various special tailored ceramics are developed with novel chemical, electrical, biological and mechanical properties. In the last three decades there has been a phenomenal transformation in microwave communication systems such as mobile telecommunication systems, satellite communication and broadcasting systems, and global positioning systems. The rapid development in microwave communication systems was made possible with the use of dielectric ceramics as enabling materials for resonators, filters and other key components in microwave components. For these applications the ceramic materials are required to have a high relative permittivity ($ε_r$), low dielectric loss, and near zero temperature coefficient of resonant frequency ($τ_f$). The combination of these requirements greatly restricts the ceramic dielectrics available for applications in microwave systems [1].

Magnesium titanate ceramics play an important role in microwave technologies such as global positioning system operating at microwave frequencies, resonators, filters, antennas for communication system and multilayer capacitors [2-5]. It is a multifaceted material of low dielectric loss with high quality factor (Q above 20000 at 8GHz) and intermediate dielectric constant ($ε_r$=17) [6]. Calcium titanate is a popular ceramic material which has a wide range of applications in industry and technology. The Calcium titanate ceramic material has high dielectric constant ($ε_r$=170) $Q\tau_f$ value ~3600 at 7GHz and $τ_f$ value ~800ppm/°C [7] and modest dielectric losses which makes it a suitable candidate for microwave applications.

In the present work, the magnesium calcium titanate ceramic materials of different compositions such as $Mg_{(1-x)}Ca_xTiO_3$ (x=0.7-0.8) were synthesized by conventional Solid State diffusion method and the phase, crystallite size, microstructure and dielectric properties were investigated.

**Experimental Procedure.** MCT $Ca_xMg_{(1-x)}TiO_3$ (x=0.7&0.8) was synthesized using Solid- state reaction method. High purity materials such as CaO (99.6% purity, Sigma Aldrich), $TiO_2$ (99.4% purity, Sigma Aldrich), and MgO (99.6% purity, Sigma Aldrich) were used as precursor materials. These materials were weighed, taken according to the composition and mixed uniformly. The mixed powders were milled for 12h in a Bill Miller (Retsch PM 200). The ground mixtures were dried and placed in alumina crucibles calcined at 1100-1120°C for 36h in air in a programmable furnace. Thus obtained calcined powders were again milled for 10h and were pressed into pellets by adding PVA
binder and by applying pressure of 8 ton using Hydraulic press. These readily formed pellets were sintered at a temperature of 1200-1250°C for 4h in the furnace with a heating rate of 10°C/min and then cooled to room temperature.

X-Ray diffractometer (Rigaku), using CuK α radiation was used to identify the crystalline phase of the samples. Microstructural analysis of the sintered samples was performed by SEM (Hitachi: S-4700) and Energy Dispersive X-Ray Spectroscopy (EDAX) for elemental composition. The dielectric constant and dielectric loss were measured by LCR meter HIOKI 3252-50 in the frequency range 1KHz to 1MHz. The dielectric constant was calculated by [8]:

$$ \epsilon_r = \frac{C * d}{\epsilon_0 * A} \qquad (1) $$

where C – is capacitance of the pellet;

d – is thickness of the pellet;

A – is the area of the cross section of the pellet;

$\epsilon_0$ – is the permittivity of free space.

## Results and Discussion.

**XRD Analysis:** The XRD profiles have shown that the sample sintered at 1150 °C (optimized) has displayed well-defined features is shown in fig. 1. XRD peaks are in good agreement with the (ICDD#22-0153) confirming the Orthorhombic structure. The maximum intensity peak occurs at 33°of 2θ for (1 1 2) reflection.

<figure><img src="image_4.png" /><figcaption>Fig. 1. XRD pattern for Mg(1-x)CaxTiO3 (x=0,0.7 & 0.8) Ceramic Materials.</figcaption></figure>

The lattice parameters of the samples CaₓMg(1-x)TiO₃ (x=0.7&0.8) are tabulated in table 1. The average crystalline size (Dₚ) is obtained using Scherer formula [9]

$$ D_p = k\lambda/\beta\cos\theta \qquad (3) $$

where k – is a constant and is equal to 0.9;

θ – is diffraction angle, λ=0.154056 nm (CuKα) and β is full width half maxima.
<table><caption>Table 1. Lattice parameters of CaₓMg(1-x)TiO₃ (x=0.7, 0.8) samples</caption><thead><tr><td>Compound</td><td>Crystal System</td><td>a(A°)</td><td>b(A°)</td><td>c(A°)</td><td>Vol(A°)³</td></tr></thead><tbody><tr><td>CaTiO₃</td><td>Orthorhombic</td><td>5.386</td><td>5.444</td><td>7.660</td><td>224.49</td></tr><tr><td>Ca₀.₂Mg₀.₈TiO₃</td><td>Orthorhombic</td><td>5.381</td><td>5.440</td><td>7.652</td><td>224.08</td></tr><tr><td>Ca₀.₃Mg₀.₇TiO₃</td><td>Orthorhombic</td><td>5.386</td><td>5.444</td><td>7.660</td><td>224.67</td></tr></tbody></table>

The dislocation density (ρ) of the samples is calculated by the formula $ρ=D^{-2}(m^{-2})$ and avg. Crystalline size are also tabulated in the table 2.

<table><caption>Table 2. Average Crystalline size and Dislocation Density</caption><thead><tr><td>Sample Name</td><td>Average Crystalline size(nm)</td><td>Dislocation Density (m⁻²)</td></tr></thead><tbody><tr><td>Ca₀.₂Mg₀.₈TiO₃</td><td>48.54</td><td>4.244x10¹⁴</td></tr><tr><td>Ca₀.₃Mg₀.₇TiO₃</td><td>53.58</td><td>3.483 x10¹⁴</td></tr></tbody></table>

**Surface Morphology:** The surface morphology is studied by Scanning Electron Microscopy (SEM). Fig. 2 shows SEM images of CaₓMg(1-x)TiO₃ (x=0.7, 0.8) which have been made at two different spots having 5000X and 10,000X magnifications in 10µm and 5µm range

respectively. In the images the grains are almost spherical in shape containing homogeneous distribution containing with distinguished boundaries with less porosity have been observed. The average grain size for the CaₓMg(1-x)TiO₃ (x=0.7, 0.8) samples was determined to be 5-6µm from the equation [10]

$$ \text{Average grain size} = \frac{1.5L}{MN} \qquad (4) $$

where L – is total test line length;

M – the magnification;

N – the total number of intercepts which the grain boundary makes with the line.
<figure><img src="image_5.png" /><figcaption>Fig. 2. SEM images of a) Mg<sub>0.3</sub>Ca<sub>0.7</sub>TiO<sub>3</sub> and b) Mg<sub>0.2</sub>Ca<sub>0.8</sub>TiO<sub>3</sub> ceramic samples.</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>Fig. 3. EDAX images of a) Mg<sub>0.3</sub>Ca<sub>0.7</sub>TiO<sub>3</sub> and b) Mg<sub>0.2</sub>Ca<sub>0.8</sub>TiO<sub>3</sub> ceramic samples.</figcaption></figure>

**EDAX**: EDAX was performed to determine the concentrations of elements such as Mg, Ca, Ti and O present in the ceramic samples. Fig. 3 gives the At% and Wt% of various elements.

**Dielectric Properties.** The dielectric properties of the sintered ceramic samples of Magnesium Calcium titanate CaₓMg(1-x)TiO₃ (x=0.7, 0.8) are studied in the temperature range from room temperature to 350°C of varying frequency of 1KHz to 1MHz are depicted in fig. 4-5. At low frequencies, the increase in dielectric constant with temperature was due to accumulation of charge at the grain boundary and at the interface of the electrode sample and the electrode which was called Space Charge Polarization [11]. As the frequency increased dielectric constant decreases due to gradual diminishing of the space charge polarization, indicating the ionic contribution. The dielectric constant is almost stable with temperature but at high temperature its value increased.
<figure><img src="image_7.png" /><figcaption>Fig. 4. Variation of Dielectric constant with Temperature at different frequencies for Mg<sub>0.2</sub>Ca<sub>0.8</sub>TiO<sub>3</sub> ceramic sample.</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>Fig. 5. Variation of Dielectric constant with Temperature at different frequencies for Mg<sub>0.3</sub>Ca<sub>0.7</sub>TiO<sub>3</sub> ceramic sample.</figcaption></figure>

The variation of dielectric loss of the sintered samples Ca<sub>x</sub>Mg<sub>(1-x)</sub>TiO<sub>3</sub> (x=0.7, 0.8) with temperature at different frequencies were shown in the fig. 5-6. At low frequency there is increase in dielectric loss with temperature nearly at 200°C and then decreases. At higher frequencies the dielectric loss is very low and almost stable. This may be an extrinsic loss dominated by secondary phases, oxygen vacancies, grain sizes and densification.

<figure><img src="image_9.png" /><figcaption>Fig. 6. Variation of Dielectric Loss with Temperature at different frequencies for Mg<sub>0.2</sub>Ca<sub>0.8</sub>TiO<sub>3</sub> ceramic sample.</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>Fig. 7. Variation of Dielectric Loss with Temperature at different frequencies for Mg<sub>0.3</sub>Ca<sub>0.7</sub>TiO<sub>3</sub> ceramic sample.</figcaption></figure>

**Summary.** The XRD confirmed the formation of Calcium Magnesium titanate and is of Orthorhombic structure. The SEM images describe the uniform distribution of grains. EDAX confirms the presence of elements of Mg, Ca, Ti and O. The dielectric constant increases with temperature at low frequencies for both the samples and at high frequencies it value is almost constant with temperature. At 1MHz frequency for both the samples exhibit very low dielectric loss which these suggest that these materials can be used in microwave applications.

**References**

[1] Wersing W. Microwave ceramics for resonators and filters, Current Opinion in Solid State & Materials Science, 1996, 1(5); 715-731, http://dx.doi.org/10.1016/S1359-0286(96)80056-8
[2] C.L. Huang, et al., Mater. Res. Bull. 37(2002) 2483-2490.

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[4] R.Z. Chen, et al., Mater. Sci. Eng. B 99 (2003) 302-305.

[5] C.C. Cheng, T.E. Hsieh, I.N. Lin, J. Eur. Ceram. Soc. 23 (2003) 2553-2558.

[6] Yuan- Fu Deng, Shi-Di Tang, Liang-Qiang Lao, Shu-Zhang Zhan, Synthesis of magnesium titanate nanocrystallites from a cheap and water-soluble single source precursor, Inorganica Chimica Acta 363 (2010) 827-829, http://dx.doi.org/10.1016/j.ica.2009.11.020

[7] R.C.Kell, A.C. Greenhem, G.C.E. Olds, Low-Loss Temperature-Stable High-Permittivity Microwave Ceramics, J.Am.Ceram.Soc. (1973) 352

[8] V. Sharon Samyuktha, T.Subba Rao, R.Padma Suvarna. Synthesis and Dielectric Properties of MgTiO3 Ceramic Material, International Journal of Engineering Research and Technology, ISSN: 2278-0181, Vol. 5 Issue 05, May-2016, http://dx.doi.org/10.17577/IJERTV5IS050349

[9] K. C. Babu Naidu, T. Sofi Sarmash, M. Maddaiah, et al., Journal of Ovonic Research 11(2), 79 (2015)

[10] M. Maddaiah, K.Chandra Babu Naidu, D.Jhansi Rani, T. Subbarao, Synthesis and Characterization of CuO-Doped SrTiO3 Ceramics, Journal of Ovonic Research 11(3), (2015) 99-106

[11] Liqiang J, Xiaojun S, Baifu X, Baiqi W, Weimin C, Hongganga F. The preparation and characterization of La doped TiO2 nanoparticles and their photocatalytic activity. J Solid State Chem. 2004;177:3375-82.