bluuebunny/crossref_metadata_2025 huggingface dataset:
Defect Induced Phonon-Branch Raman-Scattering in KTaO3
Authors: Uwe Hiromoto
Published: March 2014

Defect-induced Raman scattering of the incipient ferroelectric KTaO3 has been elicited by using a semiconducting sample as a standard. The scattering originates from finite wavevector lattice vibrations Raman-actibvated by the odd-symmetry microdistortions (OSM) probably around the center of Nb. From the scattering band shape analysis, we have found that the shape of the OSM is elliptic and the volume changes, as a function of temperature, following the estimated value from the critical Nb concentration in quantum ferroelectric KTN on assuming that the ferroelectric transition should occur when the OSM around Nb occupies the entire crystal volume.
Central Peak and Soft Mode in AgNbO3
Authors: Fontana M. D. , Kugel G. E. , Kania A. , Roleder K.
Published: March 2014

Silver niobate AgNbO3 is a perovskite compound which undergoes a complex series of structural phase transitions. Raman scattering experiments have been performed on single crystals between 300 and 650 K. The analysis of the data, in using a suitable lineshape Raman function, reveal the presence of a broad central component in addition to an underdamped soft phonon line. A very diffuse phase transition is found to be connected to the occurence of the central peak whereas a very sharp transition can be associated to the abrupt soft-phonon disappearance.
A Central Component in the Low Frequency Raman Spectra of NaNO3
Authors: Yagi Toshirou , Yasaka Hiroshi , Sakai Akira
Published: March 2014

Low-frequency Raman spectra of NaNO3 have been observed as a function of temperature in a range from room temperature to above the melting point T
m. A strong central component appears and grows up with increasing temperature. Both of the width and intensity of the component show an anomaly near the phase transition point T
c. The anomalous part of the intensity shows temperature dependence as (T
c-T)1/2 below T
c, indicating a close relation between the spectra and the order parameter in the phase transition. In terms of a spectral shape analysis using a simplified model, the origin of the central component is assigned to be a precessional free-rotation of NO3 molecules. It is derived that the precessional free-rotational motion of NO3 is essential for the order-disorder mechanism in the phase transition of NaNO3.
Study of The Soft Ferroelectric Modes by Microwave Dielectric Spectroscopy
Authors: Grigas J. , Kalesinskas V. , Paprotny W. , Brilingas A.
Published: March 2014

The paper presents a discussion on the microwave dielectric spectroscopy of the soft overdamped resonant modes of extremely low frequencies in the SbSI-type and TlGaSe2 layered crystals and relaxational soft mode dynamics in hydrogen-bonded ferroelectrics RbHSO4 and CsH2PO4.
Infrared Reflection Spectra of Ferroelectric Ammonium Sulfate
Authors: Kwun Sook-Il , Lee Soon Gul , Kim Sang Youl , Yoon Jong-Gul
Published: March 2014

The infrared reflectances of the single crystal (NH4)2SO4 have been measured as functions of temperature and crystallographic axis. It is observed that the asymmetric streching internal mode (ν3) of SO4
2 ions which has triple degeneracy at room temperature is split into two modes around the phase transition temperature along each axis, but only along the ferroelectric c-axis these two modes are split again into three modes far below the transition temperature. The triplet asymmetric bending mode (ν4) of NH4
+ ions shows no apparent change except the splitting of the peak into two in the c-axis polarized light below transition temperature. The optical constants, the mode parameters and the oscillator strengths are calculated by using Kramers-Kronig relations and the results are interpreted physically.
Far-infrared Study of Ferroelectric Soft Modes by Fourier Spectroscopy
Authors: Sawada Akikatsu , Wada Mitsuo , Fujita Kazuhiko , Toibana Hisaharu
Published: March 2014

Ferroelectric soft modes in lithium heptagermanate (Li2Ge7O15) and benzil (C6H5COCOC6H5) crystals have been studied by Martin-Puplett type far-infrared Fourier spectrometer. In lithium heptagermanate a ferroelectric soft mode with B1u(z) symmetry has been observed. In benzil a soft polar mode with E(x, y) symmetry has been observed. It is found that the oscillator strength of both modes is very small.
Observation of Ferroelectric Domains with a Scanning Electron Microscope by Decoration Technics
Authors: Beudon Didier , Boudjema El Harbi , Bihan Raymond Le
Published: March 2014

Observation of ferroelectric domain structure with a scanning electron microscope is realized after deposition of a thin film of AgCl on the studied surface of the crystal. The conditions of preparation and the determination of optimum thickness of the film are presented. The choice of correct accelerating voltage and intensity for the primary electron beam is also determined.
The observation of antiparallel and perpendicular ferroelectric domains on BaTiO3, TGS and GASH crystals by this technics is presented. In the GASH crystals, a difference of contrast between the hexagone zone and its outside is also observed. For observation of ferroelectric domains this method shows some advantages in comparison with observations made in SEM without coating the crystals and in TEM by decoration technics; for example, the polarity of the domains and their distribution can be determined.
Time-Resolved X-Ray Diffractometry and Domain Switching in NaNO2
Authors: Komori Shigeki , Minato Tadaharu , Sakashita Hirofumi , Terauchi Hikaru
Published: March 2014

Polarization reversal measurement in ferroelectric NaNO2 has been carefully carried out by using a repetitional pulsed X-ray diffractometer system developed for a time-dependent structure analysis. It is found that the X-ray scattering in- tensity of the (150) reflection which is sensitive to the polarization decreases and the width of the reflection increases after a sudden change of external electric field. It is clarified that domain wall or interface has a crucial role in nucleation-growth process. The mechanism of domain switching is discussed in terms of the characteristic times such as delay time and metastable time.
Huge Differences in Ferroelectric Curie Temperature between Growth Sectors of Boracite Crystals
Authors: Rossignol J.-F. , Rivera J.-P. , Schmid H.
Published: March 2014

The cubic (4̄3 m)/orthorhombic (mm2) phase transition temperature T
c of Mn–I, Fe–I, Zn–I, Ni–Br and Cu–Br boracite has been measured by polarized light microscopy in the pyramidal growth sectors. In either of the five compositions the (100), (110), (111) and (1̄1̄1̄) growth pyramids differ in a systematic way in T
c for each composition. A maximum difference of ∼15 K between inequivalent sectors has been observed in a same sample of both Zn–I and Cu–Br boracite.
In a (100) growth sector of Ni–I boracite the cubic (4̄3 ml')/monoclinic (m') transition is characterized by a sharp peak of dielectric constant ε', whereas in a strongly absorbing and birefringent (111) sector the anomaly is annihilated.
X-Ray Irradiation Effects on the Dielectric Constant of TGS
Authors: Nakatani Noriyuki
Published: March 2014

Dielectric constant of TGS was measured during X-ray irradiation in both the para- and ferro-electric phases with and without an external dc bias field. Experimental results are collectively interpreted by dealing with the reciprocal dielectric constant. Irradiation effects on the dielectric constant are essentially independent of both the temperature of exposure and the application of dc field. The vaccine effect against an irradiation in the ferroelectric phase, appears in specimens previously irradiated in the paraelectric phase, is not a substantial but a seeming one. Taking the absorption of X-ray into account, we can estimate the density of defects formed by the irradiation.
Reexamination of the Crystal Structure of Triglycine Sulfate
Authors: Itoh Kazuyuki , Nishikori Atsukimi , Yokomizo Hitoshi , Nakamura Eiji
Published: March 2014

The crystal structure of triglycine sulfate has been redetermined at six temperatures above and below the transition temperature, using the data collected by an X-ray automatic four-circle diffractometer. The structure is refined successfully on the basis of the split-atom method. The long-range order parameter, calculated from the difference of the probabilities occupying two molecular arrangements, is larger than that estimated from the spontaneous polarization. It is concluded that the mechanism of the phase transition is of the order-disorder type with the displacement of equilibrium atomic positions which is prominent near the transition temperature.
Neutron Diffraction Study of Ferroelectric Transition in Li2Ge7O15
Authors: Iwata Yutaka , Shibuya Iwao , Wada Mitsuo , Sawada Akikatsu , Ishibashi Yoshihiro
Published: March 2014

The crystal structure of Li2Ge7O15 in its ferroelectric state has been determined and refined as well with an R-value of 0.063 for 1202 neutron diffraction data. The crystal belongs to the orthorhmbic system with space group C2V
5-Pbc21 and unit cell dimensions a=7.36, b=16.66 and c=9.69 A (at 77 K). Atomic displacements at the phase transition (283.5 K) are evaluated in comparison with the paraelectric structure determined by Völlenkle et al., in 1970. Consequently, tiltings of GeO4 tetrahedra closely related to the soft phonon mode observed by Raman scattering and far-infrared measurements have clearly been observed.
Dielectric Ceramics for Microwave Application
Authors: Ouchi Hiromu , Kawashima Syunichiro
Published: March 2014

A review has been made to find the technical trend on the presently developed dielectric ceramics for microwave applications. Some new dielectric ceramics recently developed by authers that is (1) temperature stable and high Q materials of Ba(Zn1/3Ta2/3)O3 (BZT) and Ba(Zn1/3Nb2/3)O3–Ba(Zn1/3Ta2/3)O3 (BZNT) ceramics and (2) temperature stable and high dielectric constant materials of BaO–Sm2O3–TiO2(BST) ceramics and their applications have been introduced.
X-ray Structural Analysis of Ferroelectric Antimony-Sulfobromide
Authors: Inushima T. , Uchinokura K.
Published: March 2014

The crystal structures of ferroelectric SbSBr were determined at 294 and 11 K. The three-dimensional data were collected on a four-circle diffractometer with Mo radiation and SSD detector. The phase transition occurs at T
c=22.8 K, where the crystal structure changes from orthorhombic Pnam with z=4 to orthorhombic P
n
a21 with z=4. The T
c was determined from the temperature dependence of the intensity of 055 reflection. In the ferroelectric phase Sb and S atoms shift by 0.11 and 0.03 Å, respectively, in reference to Br atom along the c axis from T
c to 11 K.
An X-ray Study of Thermal Atomic Vibrations in Oxygen-Octahedra Compounds
Authors: Ter-Mikaelyan G. B. , Ivanov S. A. , Venevtsev Yu. N.
Published: March 2014

An X-ray diffraction study of ferro-, antiferro- and paraelectrics with perovskite, elpasolite and pyrochlore type structures has been carried out. The influence of anharmonic thermal atomic vibration on temperature dependences of temperature factors of individual sublattices, Debye temperatures and logarithms of relative integrated intensities has been studied. The potential parameters of individual sublattices αk and γk have been calculated. The conclusion has been made that in perovskites ABO3 (A=Pb, B=Ti, Zr), elpasolites A2Ca2+B6+O6 (A=Ba, B6+=Re, Te) and pyrochlores A2B2O6X (A=Cd, B=Nb, X=O, S), A-sublattice should be considered as ferroelectrically active one, and that deviations from harmonic behaviour for A-cations seem to be appreciable.
Growth and Some Properties of Ferroelectric Tungsten Bronze Niobate Solid Solution Crystals
Authors: Chen H. C. , Chen F. S. , Song Y. Y. , Zhang P. L. , Zhong W. L.
Published: March 2014

Single crystal growth of niobate solid solution of ferroelectric tungsten bronze with general formula A1.2Nb2O6 in which A sites are all occupied by alkai, alkaline earth, transtion metal and rare earth ions have been studied in detail. The significant changes in lattice constants, dielectric properties, growth habits and others can be obtained with changes
of ions.
Preparation of Oriented PbTiO3 Ferroelectric Thin Films on Silicon
Authors: Okuyama M. , Ueda T. , Hamakawa Y.
Published: March 2014

A series of technical data on the preparation of oriented PbTiO3 ferroelectric thin films on Si wafer by rf sputtering have been presented. Two kinds of approaches have been tried to improve crystalline properties of the PbTiO3 films. Firstly, highly-oriented CaF2 and SrF2 films have been grown on Si wafer as a buffer layer by electron beam evaporation at 400–600°C. The PbTiO3 film on the SrF2/(100) Si and CaF2/(111) Si have been oriented in (100) and (110) & (101) directions, respectively. Secondly, negative DC bias voltage has been applied to the Si substrate during the sputtering of PbTiO3. The obtained films are highly-oriented and their dielectric properties are improved with increase of the bias voltage. Surface of the obtained film is very smooth.
Crystals of the Bi2GeO5–Bi4V2O11 System
Authors: Bush. A. A. , Koshelayeva V. G. , Venevtsev Yu. N.
Published: March 2014

A possibility of formation of new ferroelectric compounds and solid solutions has been concluded in particular on the basis of the established relationship between the crystal structures of Bi2BO55(B=Ge, Si) and Bi2BO6(B=W, Mo). Single crystals of new Bi4V2O11 compound and Bi4(Ge1-x
V
x
)2O10+x
solid solutions were synthesized. X-ray studies as well as studies of some dielectric and pyroelectric properties of crystals were carried out. It was found that the crystal structures of these new compound and solid solutions are related to those of Bi2BO5(B=Ge, Si) and ·Bi2BO6(B=W, Mo). The reversible first order phase transition was revealed at 550 K for Bi4GeVO10.5 grown from 3Bi2O3·2GeO2·V2O5 melt
Non-Centrosymmetrical Phases in Compounds of a New Group of Li3MeO4 and Li4MeO4F(Me=NbV, TaV) Oxides and Oxyfluorides
Authors: Stefanovich S. Yu. , Strukov B. A. , Leonov A. P. , Agulyansky A. I. , Kalinnikov V. T.
Published: March 2014

Polymorphism of double oxides and oxyfluorides–Li4NbO4F, Li3NbO4, Li4TaO4F and Li3TaO4 was studied by the SHG method. Non-centrosymmetrical phases of Li4NbO4F and Li3NbO4 pass irreversibly into the centrosymmetrical phase at 800-850 and 1000°C, respectively. For Li4TaO4F and Li3TaO4 reversible transitions were found at 680 and 660°C respectively. In the vicinity of the phase transition optical susceptibility obeys the law χ∼(T
c–T)1/2.
Effects of Domain and Electric Field on 14N NQR in NaNO2
Authors: Choh S. H. , Park Y. J. , Kim H. K.
Published: March 2014

The effects of the domain structure and the applied electric field on 14N NQR have been investigated in conjuction with anomalies found in quadrupole parameters between a single crystal (S
1) and powder. Though there are differences in the domain structure in two crystals (S
1 and S
2), photographed with the polarizing microscope, no detectable differences of the resonance frequency and the line width are recorded. The frequency shift due to the electric field up to 30 kV/cm for the ν+ and ν- -line is 10 and 4.5 Hz·cm/kV at 77 K, respectively. From these results the anomalies observed with the S
1 crystal seem to be due to the microscopic aspect in the NaNO2 crystal rather than the macroscopic nature such as the domain structure of the crystal.
BaTiO3 as a Biased Paraelectric
Authors: Burns Gerald , Dacol F. H.
Published: March 2014

With the assumption that the ferroelectric tetragonal phase of BaTiO3 can be treated as a biased cubic phase, we have found the temperature dependence of the electrooptic coefficient and the electrostrictive coefficient.
Photoacoustic Study on Phase Transition in FE Ceramics
Authors: Qing-Rui Yin , Guang Li , Zhi-Wen Yin
Published: March 2014

The phase transitions in FE ceramics, such as Pb(Zr,Ti,Sn)O3 (PSZT), transparent PLZT and Li1-x
Na
x
NbO3(LNN), were studied with the photoacoustic technique. The features of the differences in phase transition in these ceramics are revealed. The photoacoustic technique is confirmed to be very sensitive to phase transition. The results could be explained thermoelastically.
Photoluminescence of Eu3+ in Layered A2B2O7 Ferroelectric Crystals
Authors: Mochida Tetsuya , Ohi Kikuo
Published: March 2014

The excitation and emission spectra of Eu3+ in the ferroelectric Sr2Ta2O7, Sr2Nb2O7 and La2Ti2O7 have been measured. The crystal field symmetry around the Eu3+ is discussed in connection with the layered perovskite structure of these oxides. It has been found that the 5
D
0-7
F
2 emission lines in Sr2Ta2O7:Eu3+ and Sr2Nb2O7:Eu3+ change with the structural phase transition.
Photoluminescence and Photocurrent in KTaO3 Single Crystal
Authors: Sekiguchi Nobuhiro , Tokunaga Kenji , Watanabe Koichi , Yamaichi Eiji , Imamiya Koji , Ohi Kikuo
Published: March 2014

The photoluminescence in KTaO3 single crystal was observed under the illumination of the band-gap light. The emission spectra consist of two broad bands which have the peaks at 2.2 eV and 2.6 eV. The decay of the photoluminescence was measured using N2 pulse laser. The decay of the luminescence at 2.6 eV is explained by the recombination of electrons trapped on donors with holes trapped on acceptors. The photoluminescence is discussed in comparison with the temperature dependence of the photocurrent.
Protonic Conductivity in Li(N2H5)SO4 Single Crystals
Authors: Salman Fathy Esmail , Hilczer Bozena , Pawlaczyk Czeslaw
Published: March 2014

Complex impedance of L
i(N
2
H
5)S
O
4 was measured in the frequency range 20 Hz\div500 KHz from 290 K to 455 K. Our results confirm the model of one dimensional protonic conduction with extrinsic barriers related with defects proposed by Schmidt et al. An activation energy of 0.48 eV is assigned to the extrinsic c-axis protonic conduction, whereas 0.35 eV refers to the intrinsic conduction. There is an indication of a structure change at ∼433 K.
Neutron Scattering Study of NaN3
Authors: Nishi Masakazu , Ito Yuji
Published: March 2014

Many experimental and theoretical studies were directed to elucidate the structural phase transition of NaN3 taking place at T
c=293 K. Our particular interest lies in the controversy whether the librational motion of N3
-(azide) ion is essential to this structural phase transition or not. The present neutron scattering results unambiguously shows a softening taking place in the transverse acoustic phonon propagating along the c* direction, whereas the librational mode of N3
- molecule does not show any significant temperature variation at the transition point. Accordingly we conclude that the structural phase transition of NaN3 is of the displacive type, in which the motions of Na+ ions are involved, whthout accompanying the corresponding softening of the librational motion of N3
- ions.
The ReO3-Related Structure Ferroelastic Fluorides
Authors: Ravez Jean , Mogus-Milankovic Andrea
Published: March 2014

A rhombohedral-cubic transition has been detected in some Re03-related structure fluorides by calorimetric, X-ray diffraction and optical measurements. The structural relation between the low and high temperature phases has allowed to predict this transition to be a ferroelastic-prototype one. The observation of ferroelastic domains and their disappearance above Curie temperature are in good agreement with this assumption.
The seven studied compounds can be separated in three very close families: AlF3, TF3 (T=Ti, V, Cr, Fe, Ga) and InF3. In the second family the spontaneous strain e
s and the Curie temperature T
c have been correlated with the size of the T
3+ cations: the values of e
s and T
c increase as r
T3+
decreases.
Ferroelastic Phase Transitions in Lead Orthophosphovanadates Pb3P2xV2-2xO8
Authors: Kiat J. M. , Calvarin G. , Garnier P. , Grégoire P.
Published: March 2014

The phase transitions γ(R3̄m)→β(P21/c)→α(A2) of mixed compounds Pb3P2x
V2-2x
O8 were studied both on powder samples and single crystals. X-ray results show there is no tricritical point in the composition range x=0.0–0.6. On the other hand a coexistence of phases is observed in a wide temperature range (martensitic behaviour) when x\geqslant0.2, and the β→α and γ→β transitions no more occur when x\geqslant0.24 and x\geqslant0.28 respectively. The structural mechanism of the γ→β transition is discussed in relation with existence of lone pairs of Pb(II) ions located between the structural layers.
Experimental Studies on Mixed Ferro-Antiferroelectric Glasses
Authors: Courtens Eric
Published: March 2014

The growth, structure, and dynamics of RbH2PO4–NH4H2PO4 mixed crystals are reviewed. In the intermediate concentration range, the built-in frustration of these materials prevents the ordinary ferroelectric or antiferroelectric transitions, whereby the disordered acid-proton sublattice freezes into a glass. This has been observed with a number of experimental techniques, including dielectric dispersion, optical birefringence, X-ray diffraction and scattering, Raman and Brillouin scattering, NMR, and more recently, specific-heat and neutron scattering. The variety of techniques applicable to this system has allowed the observation of polarization freezing over about 17 orders of magnitude in frequency. This freezing is well described phenomenologically by the Vogel-Fulcher law, while other laws proposed for spinglasses are less successful. Recent hypersonic-relaxation measurements point to the existence of a frozen polarization component at temperatures already much above Vogel-Fulcher freezing, while neutron diffused scattering reveals that the tendency to form superstructures is not static.
Chaotic Behaviour of Nonlinear Electromechanical Resonators (Rochelle Salt)
Authors: Beige H. , Albers J. , Petersson J.
Published: March 2014

For a longitudinally vibrating bar and a series-resonance circuit the experimental observations of the phase portrait show a chaotic behaviour. In the first case the nonlinear nature of the resonant system is determined by the nonlinear elastic coefficient of third- and fourth-order of Rochelle salt. The nonlinear properties of the series circuit containing a Rochelle salt capacitance and a linear inductance can be described by the nonlinear dielectric coefficient of thrid- and fourth-order.
Phase portraits calculated with our data for the corresponding linear and nonlinear coefficients are in a good agreement with experimental results.
Piezoelectric Properties of Bismuth Layer-Structured Ferroelectric Na0.5Bi4.5Ti4O15 Ceramic
Authors: Takenaka Tadashi , Sakata Koichiro , Toda Kohji
Published: March 2014

Piezoelectric properties of the grain-oriented Na0.5Bi4.5Ti4O15 (NBT) ceramic, belong to the bismuth layerstructured ferroelectric (BLSF) ceramics are studied from applicational viewpoints on grain orientation prepared by the hot-forging (H.F.) method. The MnCO3 (0.1 wt%) doped NBT (NBT+Mn(0.1)) ceramic can stand the high temperature poling process, because of the high resistivity.
The grain orientation (H.F.) makes the piezoelectric properties of NBT+Mn(0.1) ceramic much more pronounced than those of the non-oriented (O.F.) ceramic. Coupling factors k
33 and k
15, along with piezoelectric constants d
33, d
15, g
33 and g
15, of the H. F. NBT+Mn(0.1) ceramic are enhanced, and their anisotropies in k
33/k
31 and k
15/k
24 are emphasized. A bulk wave delay line oscillator using the ceramic substrate is demonstrated.
Grain Size Dependence of Electrostriction in PMN Ceramics
Authors: Uchino Kenji , Tatsumi Masaichi , Hayashi Iwao , Hayashi Teru
Published: March 2014

The electrostriction of Pb(Mg1/3Nb2/3)O3-based ceramics is strongly affected in both magnitude and hysteresis by their preparation history. This paper describes the factors determining the electrostrictive response, putting emphasis on the grain size dependence. The electrostrictive strain and the hysteresis decrease mainly with decreasing maximum grain size, even if the average grain size is maintained nearly constant.
Electrostriction Properties of Oxygen Octahedron Ferroelectrics
Authors: Asadipour P. , Kumar U. , Jang S. J. , Bhalla A. S. , Cross L. E.
Published: March 2014

For the materials with diffuse phase transitions it is suspected that the long-range coupling may be weakened by local composition fluctuations and thus near T
c strong local fluctuations could develop in P
s. In the case of Sr0.61Ba0.39Nb2O6 (SEN) measurements of the electric polarization. P
s, thermal strain x
1, and x
3, dielectric constant, K
3 and optical birefringence are used to confirm that the polarization P
3
2 is not zero for a range of temperature above T̄
c The values of P
3
2 deduced from x
i vs T and birefringence vs T, the two independent methods are in good agreement indicating substantial polarization fluctuations which decay slowly above the mean Curie temperature. T̄
c.
Modulated Structure and Magnetic Resonance Spectrum in the Incommensurate Phase of A2BX4 Type Crystals
Authors: Azuma A. , Kobayashi T. , Suhara M.
Published: March 2014

The Landau theory was applied to interprete the temperature dependence of the magnetic resonance spectrum in the incommensurate and commensurate phases of A2BX4 type crystals. Taking into account the local electric field at the probe sub-lattice, we demonstrated the systematic temperature change in the splitting and shape of resonance lines and clearly reproduced the reported results in K2SeO4:SeO4
-, K2SeO4:VO2+ and Rb2ZnCl4 crystals.
Phase Transitions of Solid Solution [(CH3)4N]2Zn1-xMxCl4 Single Crystals with M=Mn, Co.
Authors: Perret R. , Godefroy G. , Arend H.
Published: March 2014

Solid solutions crystals of [(CH3)4N]2Zn1-x
M
x
Cl4 with M=Mn, Co and 0<x<1 were grown. Their phase diagram was plotted from differential scanning calorimetry measurements and known crystallographic data of the pure components. The observed phase sequences are compatible with a reduced pressure vs. temperature diagram characterising all known pure [(CH3)4N]2MX4 compounds.
Lattice Deformations in the Successive Phase Transitions of (NH4)2ZnCl4 and {N(CH3)4}2ZnCl4
Authors: Deguchi Kiyoshi , Motegi Hiroshi , Nakamura Eiji , Fukunaga Hideki
Published: March 2014

Polarization microscopic observations of (NH4)2ZnCl4 have revealed a domain structure in o-plates in the phases III (46∼91°C), IV (-5∼46°C) and V (-10∼-5°C) and another one in c-plates in the phase V. The former domain structure does not change at the III–IV and IV–V phase transitions and disappears at about 70°C. Similar observations of [N(CH3)4]2ZnCl4 have revealed different domain structures in a- and c-plates in the phase IV (-92∼3°C) and in a- and b-plates in the phase V (-112∼-92°C). The lattice strains associated with these domains except two in [N(CH3)4]2ZnCl4 are determined with the X-ray double-crystal method. Discussions are made on the crystal symmetries of the intermediate phases of both materials. The temperature dependences of the spontaneous shear strains observed in the intermediate phases of both materials are found to be different from those expected from the usual Landau-type free energy.
Dielectric Critical Slowing-Down in Incommensurate Ferroelectric Transition Point of K2SeO4-Type Crystals
Authors: Horioka Masakiyo , Sawada Akikatsu
Published: March 2014

The dynamic susceptibility X(ω) in the incommensurate phase of K2SeO4-type crystals has been derived from the phenomenological kinetic equations of the Landau-Khalatnikov type. The critical slowing-down of the polarization fluctuation which has been observed around the incommensurate-commensurate transition temperature can be explained as the softening of the phase mode of discommensuration lattice. The polydispersive nature of the relaxation time observed in the incommensurate phase is discussed on the basis of the present model.
NMR Study of the Temperature and Electric Field Dependence of the Soliton Density Near the Lock-in Transition of Rb2ZnCl4
Authors: Petersson J. , Schneider E.
Published: March 2014

The frequency distribution of the 87Rb NMR 1/2 ↔-1/2 central transition is measured in the incommensurate (IC) and commensurate (C) phases near the lock-in transition at T
c of high quality single crystals of Rb2ZnCl4 (RZC). In a temperature region not exceeding 15 K above T
c some centers of intensity termed C lines are detected above the incommensurately broadened background spectrum at frequencies where in the lock-in C phase discrete lines are observed. The intensities of the C lines are related to the soliton density. In the region around T
c the temperature and electric field dependence of the soliton density is determined. The experimental results are explained by introducing a general definition of the soliton density describing the experimental NMR results adequately not only in the narrow soliton limit.
Analysis of the Raman Spectrum of the Higher Frequency Modes of Rb2ZnCl4
Authors: Katkanant V. , Ullman F. G. , Hardy J. R.
Published: March 2014

The stretching-region (250–330 cm-1) internal modes of Rb2ZnCl4 were studied by Raman-scattering from 190 to 330 K. Four lines, peaking at about 275, 285, 295 and 304 cm-1 are clearly resolved below the normal-to-incommensurate phase transition (307 K in these measurements); above 307 K, the four merge into three and the 285 cm-1 peak is no longer detectable. The derivatives of these spectra were fitted to the derivative of an overlapped, spectrometer-corrected, four-Lorentzian lineshape. The resulting temperature dependence of the integrated intensity of the 285 cm-1 peak decreases by at most a factor of 3 up to 305 K whereas the square of the order parameter in this range decreases by a factor of about 50. Thus, its disappearance above 307 K is as yet unexplained.
Kinetic Process of Commensurate-Incommensurate Transition in K2ZnCl4
Authors: Ema Kenji , Izumit Haruhiko , Hamano Katsumi
Published: March 2014

The time change of the dielectric constant at twenty-six different frequencies covering the dispersion region was traced during the C-to-INC and INC-to-C transitions which were triggered by a temperature jump. In both cases the static dielectric constant increased first, reached a maximum and then decreased. The relaxation frequency showed a monotonical increase during the C-to-INC transition and a monotonical decrease during the INC-to-C transition. The results suggest that the spacing between the discommensurations is gradually narrowed during the C-to-INC transition and widened during the INC-to-C transition.
Relaxation of the Modulated Structure near the Lock-in Transition in K2ZnCl4
Authors: Mashiyama Hiroyuki , Kasatani Hirohumi
Published: March 2014

The time variation of the dielectric constant and the satellite reflections has been measured following the incommensurate-commensurate transition in K2ZnCl4. The dielectric constant approaches the steady value with a exponential function of the square root of time. X-ray diffraction study has revealed that the dielectric relaxation is accompanied by the change of satellite and diffuse scatterings. The slow relaxation is considered to reflect a nucleation kinetics of discommensurations under the influence of crystal imperfections.
X-ray Intensity Measurement of Satellites in Quartz Intermediate Phase
Authors: Gouhara K. , Kato N.
Published: March 2014

The satellite reflections and the diffuse scattering of the intermediate phase (IP) of quartz in the α–β phase transition, particularly associated with (01̄, 1) Bragg reflection, were studied by the X-ray intensity measurements. The temperature was well controlled (±0.05 K). The individual satellite of a single rotation domain is angularly sharp (30 sec. at most) over the whole range of IP. The integrated intensity depends upon the modulation vectors q

i
, and the temperature. A weak hump of the diffuse scattering starts to appear gradually from 11 K above the critical point T
Q in the cooling run.
An Optical Study of α-β Phase Transition in Quartz
Authors: Yamada Noboru , Ikeda Takuro
Published: March 2014

The rotatory power of quartz was determined in the wide temperature range 20°∼650°C. The α\rightleftarrowsINC transition was associated with a discontinuous jump (∼0.3°/mm) and a thermal hysteresis (0.7°∼0.9°C), whereas the INC\rightleftarrowsβ transition was recognized only by a slight change of temperature-gradient. Such a typical feature was observed in synthetic quartz specimen. Natural quartz specimen showed an additional anomaly in the INC-phase. Furthermore the annealing treatments of specimens caused complicated step-wise temperature dependence of transient nature around the phase transitions.
Anomalous Incommensurate Soft Mode Damping in Cd2Nb2O7 and K2SeO4
Authors: Kolpakova N. N. , Březina B. , Sher E. S.
Published: March 2014

Slowing down of decline of the Raman soft mode damping in the incommensurate phase as well as a steep drop of the soft mode integrated intensity at the incommensurate-commensurate phase transition show the existence of the phase mode in the incommensurate phase.
Temperature Dependence of Spontaneous and Induced Polarization of Betaine Calcium Chloride Dihydrate
Authors: Klöpperpieper A. , Rother H. J. , Albers J. , Müser H. E.
Published: March 2014

Betaine calcium chloride dihydrate (BCCD) is ferroelectric at low temperatures. A sequence of eight transition points separates different commensurate and incommensurate phases with complicated dielectric behavior. On BCCD and the deuterated compound dielectric and caloric measurements are performed to establish the temperature dependence of dielectric constants, coercive fields, critical fields, spontaneous polarizations and induced sublattice polarizations. Additional data about crystal growth and characterization are presented.
Quasi-Static D–E Hysteresis Loops on SC(NH2)2 and SC(ND2)2 at the Phase Transition Regions
Authors: Hatano Jun , Kume Nobuyuki , Kubota Kenji , Tsukamoto Takeyo , Futama Hideo , Gesi Kazuo
Published: March 2014

Phase boundaries of SC(NH2)2 have been determined by X-ray diffraction intensity and dielectric constant measurements under electric bias field. Results similar to the case of SC(ND2)2 have been obtained in SC(NH2)2.
Ferroelectric D–E hysteresis loops at the phase transition regions have been observed by a computer-controlled Sawyer-Tower bridge in which quasi-static trace of field can be attained. Peculiar triple-like hysteresis loops have been observed at a narrow temperature range just outside of the ferroelectric phase. The width of the temperature range becomes narrow with the decreasing rate of impressing the field.
The Incommensurate Metastable Phase, Nonequilibrium Processes and Memory Effect in the Ferroelectric NH4HSeO4
Authors: Aleksandrova I. P. , Moskvich Yu. N. , Razanov O. V. , Sadreev A. F. , Seryukova I. V. , Sukhovsky A. A.
Published: March 2014

The instability of the incommensurate phase in NH4HSeO4 was revealed using 77Se high resolution NMR. The nonequilibrium processes accompaning the long-range order destruciton and memory effect were investigated using both NMR and dielectric measurements. The three-dimensional version of the topological phase transition accounting the interaction of three-dimensional solitons with the point defect is developed to explain the experimental data.
Pressure Dependence of the Ferroelectric Transition in Copolymers of Vinylidene Fluoride and Trifluoroethylene
Authors: Koizumi Naokazu , Murata Yukinobu , Haikawa Noriko
Published: March 2014

Effect of the hydrostatic pressure p on the ferroelectric transition T
t in copolymers of vinylidene fluoride VDF and trifluoroethylene TrFE with 47.2 and 35.4 mol-% TrFE has been investigated for dielectric behavior and thermal expansion. The permittivity peak and the abrupt increase in thermal expansion at the transition shifted markedly to higher temperature with increasing pressure. The pressure dependence of the transition dT
t/dp observed was 0.31 KMPa-1 on heating for 47.2 mol-% TrFE copolymer and 0.38 KMPa-1 on heating and 0.40 KMPa-1 on cooling for 35.4 mol-% TrFE Copolymer. These values of dT
t/dp were consistent with those calculated by the Clausius-Clapeyron relation. The bulk modulus evaluated from the expansion vs pressure curve exhibited a conspicuous minimum at the ferroelectric transition as found for other physical properties.
Polarization Reversal of Ferroelectric Polymers
Authors: Ikeda Susumu , Fukada Tomohiro , Jimbo Masashi , Koyama Kiyohito , Wada Yasaku
Published: March 2014

Two kinds of effects of the depolarization field in a ferroelectric crystallite of the polymer on its polarization reversal switching are discussed. Space charges on the crystallite-amorphous phase interface reduce the depolarization field, decelerating the polarization reversal. In the course of polarization reversal, this interfacial polarization charge between reversed and unreversed domains increases with increasing fraction of the former, resulting in acceleration of the polarization reversal of the unreversed domain.
Ferroelectric Phase Transition of VDF/TrFE Copolymer at High Pressures
Authors: Matsushige Kazumi , Tagashira Katsuharu , Horiuchi Toshihisa , Taki Seiji , Takemura Tetsuo
Published: March 2014

High pressure ultrasonic and D-E hystresis measurements were performed on a vinylidene fluoride-trifluoroethylene (VDF/TrFE) copolymer with 54 mol% VDF content to investigate the pressure effect on physical properties accompanying wiht a ferroelectric phase transition. Differing from the results at atmospheric pressure where the ferro-to-paraelectric phase transition proceeded simply in one-step, this copolymer exhibited at 350 MPa two-step temperature variations in ultrasonic velocity and absorption, and remanent polarization upon the ferroelectric phase transition. These results agree well with the previous results of DTA and X-ray diffraction experiments, suggesting that the changes in the nature of the ferroelectric phase transition is attributed to the pressure-induced structural transformation.
Structural Phase Transition in Ferroelectric Vinylidene Fluoride-Trifluoroethylene Copolymers
Authors: Tashiro Kohji , Kobayashi Masamichi
Published: March 2014

Crystal structural changes occurring in the ferroelectric phase transition have been described for a series of vinylidene fluoride-trifluoroethylene copolymers and poly (vinylidene fluoride) form I. The transitional behaviors were found to be much affected by the VDF molar content of the copolymers.
Application of PVDF Thick Films in Large-Area Hydrophone Arrays
Authors: Henriquez T. A. , Ting R. Y.
Published: March 2014

As the availability of PVDF thick films increases in recent years, this material is becoming more attractive for large-area hydrophone applications. By taking advantage of the long-strip configuration of PVDF, a 4×4 hydrophone array was fabricated. The electrode layers on the strip were patterned to give four 6.35 cm×6.35 cm square elements. Four strips were aligned in one direction in the bottom layer, and four other in the perpendicular direction in the top layer. Each element was then connected electrically in parallel, such that the two layers of PVDF formed the desired 4×4 array. The array was extensively tested, and the results of vibrational, acoustical and phase measurements are discussed.
Ferroelectric Polymer for Thermodielectric Energy Conversion
Authors: Tiwary H. V.
Published: March 2014

There have been few reports on the application of ferroelectric materials for direct thermal to electrical energy conversion. The basic principle utilizes the conversion of heat energy directly into electrical energy with or without utilizing the high dielectric constant anomalous peak values around the transition temperature of ferroelectrics.
Thin-film form of the material and polymers are supposed to give suitably superior conversion efficiency. The choice of material as sheets of ferroelectric polymer polyvinyledene (PVF2) has been characterised.
General analysis indicates better conversion efficiency with respect to other ferroelectric films or polymer sheets with maximum limit of power output. The energy ratio i.e. the ratio of the input heat energy to the obtainable electrical energy is assessed to be around 0.861.
Solitons and their Attractive Interaction in Ferroelectric Liquid Crystal–SmC*-SmC Transition in an Electric Field–
Authors: Yamashita Mamoru
Published: March 2014

Phase transition between chiral smectic C and smectic C phases is interpreted as a condensation of soliton which is a kink of an order parameter. Owing to variable magnitude of order parameter, an interaction between solitons can be attractive and accordingly the transition becomes discontinuous. By analyzing so-called soliton lattice, the phase boundary in an electric field versus temperature plane is determined, which can give a basis of discussion on a reentrant phase transition observed just below the transition temperature between chiral smectic C and smectic A phases.
Dynamical Aspects of Switching between Surface Stabilized States in Smectic C* Ferroelectric Liquid Crystal
Authors: Ouchi Yukio , Ishikawa Ken , Takezoe Hideo , Fukuda Atsuo , Kondo Katsumi , Era Susumu , Mukoh Akio
Published: March 2014

The switching process in a surface stabilized ferroelectric liquid crystal (SSFLC) cell under triangular wave voltage is studied by taking stroboscopic micrographs. Interior ±2π disclination motions and surface layer changes with surface disclinations are observed even in a uniform-state favored cell. The asymmetric semicircular shape of the ±2π disclination loop is observed under low frequency triangular waves of 0. 1 Hz. The loop becomes elongated hexagonal, when the frequency increases to 1 Hz or 10 Hz.
Two-Dimensional Order in Liquid Crystals: a Phenomenological Approach
Authors: Tolédano P. , Tékaïa R.
Published: March 2014

The two-dimensional ordering reported for a number of smectic and discotic phases is discussed in the framework of the Landau theory. It is shown that, within a phenomenological approach, distinction should be made between the longrange bond-orientational order, the in-plane positional order, and the orientational (tilting) ordering of the molecules. Accordingly, the configuration of the smectic liquid crystal phases B

H
, C, F, and smectic crystal phases I, J, G, K, E are shown to be related to irreducible degrees of freedom of definite parent smectic phases. Along the same line, discotic phases are shown to be induced by specific irreducible representations of the nematic phase.
KH2PO4-Type Crystals: A Displacive Phase Transition Induced by Proton Disorder Behavior
Authors: Simon Patrick , Gervais François
Published: March 2014

The infrared reflectivity spectra of KH2PO4, RbH2PO4 and KH2AsO4 for the electric field polarized along the ferroelectric axis are reported and compared. For the phosphate compounds, the phonon responses are deduced from the best fit of the factorized form of the dielectric function to the experimental spectra. Results evidence the softening of an internal mode (V
4c), which is destabilized by proton motions between their two quasiequilibrium positions. It couples with lowerfrequency external modes, and finally induces the paraelectric-ferroelectric phase transition, which appears as displacive, though induced by an order-disorder mechanism.
Polarization Dependence of O–H–O Raman Bands in KH2PO4 Crystal
Authors: Choi Byoung-Koo , Kim Jong-Jean
Published: March 2014

The O–H–O Raman bands of the paraelectric KH2PO4 crystal were found to have weak components of E(α
x
z
) and A
1(α
z
z
) symmetries in addition to the strong components of A
1(α
x
x
+α
y
y
) and B
1(α
x
x
-α
y
y
) symmetries. Implications of this observation of weak components are discussed in terms of the off-axis equilibrium sites of hydrogen in O–H–O as well as the strong coupling theory.
Raman Scattering in NH4H2PO4 and ND4D2PO4
Authors: Kasahara Masaru , Tatsuzaki Itaru
Published: March 2014

Raman spectra of NH4H2PO4, and ND4D2PO4 were observed in both the paraelectric (PE) and antiferroelectric (AFE) phases. It was found that the internal modes of both ions, H2PO4
-(D2PO4
-) and NH4
+(ND4
+) ions, have a momentary site symmetry in common: C2 in the PE phase and C1 in the AFE phase. These results for H2PO4
-(D2PO4
-) ions show that the lateral Slater configurations cannot be detected in the PE phase. On the other hand, the lateral Slater configurations do exist in the AFE phase. Furthermore, the site symmetry C2 of NH4
+(ND4
+) ions in PE phase reveals that these ions are deformed from regular tetrahedral symmetry in the crystal lattice even in the PE phase.
Brillouin Scattering of Paraelectric KH2PO4 under Applied Uniaxial Stress
Authors: Takagi Y. , Zgonik M. , Copic M. , Lavrencic B. B.
Published: March 2014

The Brillouin scattering spectra of XY shear phonon in KH2PO4 under an applied XY shear stress have been studied in the neighborhood of the ferroelectric transition temperature. The acoustic phonon is overdamped near T
c, but become underdamped under the applied shear stress. The observed increase of elastic constant C
66 with increasing XY shear stress is similar to dependence on electric fields. In the case of Δ
T(≡T-T
c)<∼0.05 K, application of stress caused a transition not to have a soft acoustic phonon.
Symmetry Change of 77Se Hyperfine Components of ESR Spectrum of SeO4
3- Radicals in Deuterated NH4H2PO4
Authors: Fukami Takanori , Akahoshi Shin , Hukuda Kenzi
Published: March 2014

D-rate dependence (0-70%) of the 77Se hf line-positions of SeO4
3- radicals in deuterated NH4H2PO4 is reported. In the
paraelectric phase, on cooling, the symmetry of the angular dependence changes from high symmetry to low-symmetry A (which is similar to that for KDP or DKDP), but no remarkable deuteration effect is observed. In the antiferroelectric phase, the angular dependence for ADP still shows the low-symmetry A, while that for DADP (D70%) shows the lowsymmetry B which is compatible with the AFE order (the Nagamiya's model) of the ammonium salts. From this large deuteration effect on the SeO4
3- it is suggested that the AFE distortion of the PO4
3- radical in the D salts is larger than that in the H salts.
Theoretical Studies on Phase Transitions in RDP-ADP Mixed Crystals
Authors: Matsushita Eiko
Published: March 2014

A theory of various phase transitions in RDP-ADP mixed crystals is developed on the basis of Ising pseudo-spin model for the proton system. The phase diagram and unusual physical properties of this system derived theoretically are in good agreement with the experimental results.
Dielectric Constant of Rb0.25(NH4)0.75H2PO4 below 1 K
Authors: Miura Yu-ichi , Takashige Masaaki , Terauchi Hikaru , Takano Yasumasa , Ishimoto Hidehiko , Ogawa Shinji
Published: March 2014

The dielectric constant ε of a mixed crystal of hydrogenbonded ferroelectric RbH2PO4 and antiferroelectric NH4H2PO4 has been measured along the a-axis at temperatures between 0.027 and 1.0 K. The results show, for the first time, the existence of two-level tunneling systems in these mixed crystals.
Thermal Properties of the Frustrated Rb0.52(ND4)0.48D2PO4 System at Low Temperatures
Authors: Lawless W. N. , Schmidt V. H.
Published: March 2014

Specific heat and thermal conductivity data, 1.5–35 K, are reported on the mixed (frustrated) ferroelectric-antiferroelectric crystal Rb0.52(ND4)0.48D2PO4. A glasslike linear term in the specific heat is resolved below 5 K and ascribed to random electric fields caused by the random distribution of Rb ions, in good agreement with the theory of McWhan et al. A maximum in C/T
3 at 13.5 K is attributed to dispersionless motions of the deuterium ions, by analogy with KDP. In contrast to the specific heat, the thermal conductivity is not glasslike, displaying a maximum at 12.5 K of 37 mW cm-1K-1. At lower temperatures, the behavior of the thermal conductivity is tentatively ascribed to resonant phonon scattering from the Rb–ND4 system. The Debye temperature for the crystal is 303 K, in reasonably good agreement with extrapolations based on θD for KDP.