Acoustic and dielectric anomalies in the temperature range of a ferroelectric phase transition in glycine phosphite crystals

The acoustical and dielectric properties of glycine phosphite crystals are investigated in the temperature range of a ferroelectric phase transition. The acoustic anomalies for longitudinal waves along the X, Y, and Z crystallographic axes (where Y is the spontaneous polarization axis) are analyzed in the framework of the Landau theory. It is shown that pronounced acoustic anomalies of the velocity can be quantitatively described within the pseudoproper ferroelectric phase transition model with due regard for the long-range dipole-dipole interaction. For longitudinal acoustic waves propagating along the polar crystal axis, the striction anomaly of the velocity is only partly suppressed by the long-range dipole-dipole forces and an abrupt jump in the velocity is observed in the vicinity of the phase transition. The temperature coefficients of the velocity in the paraphase are determined. The striction contribution and the contributions biquadratic in the order parameter and in the strain to the velocity anomaly are separated.     

Acoustic properties of glycine phosphite crystals with an admixture of glycine phosphate

Acoustic and dielectric anomalies in the region of the ferroelectric phase transition in crystals of glycine phosphite (GPI) with a 2 mol % admixture of glycine phosphate (GP) are studied. The acoustic anomalies were found to differ strongly from those observed in nominally pure glycine phosphite crystals. A theoretical analysis of the acoustic and dielectric properties of the crystals was carried out within the model of a pseudoproper ferroelectric phase transition. It is shown that the acoustic anomalies, as well as the temperature dependences of the dielectric constant (for various external electric fields) and pyroelectric current observed in the vicinity of the phase transition in GPI-GP crystals, can be adequately described when the macroscopic polarization present in these crystals above the phase transition temperature is taken into account. The thermodynamic-potential parameters describing electrostriction and the biquadratic relation between the polarization and strain turned out to be close to those characterizing a nominally pure GPI crystal. An irreversible phase transition was observed to occur in GPI-GP crystals at T = 240 K, i.e., above the ferroelectric phase transition temperature.     

Phase transition in sarcosine phosphite single crystals

Single crystals of sarcosine phosphite (SarcH₃PO₃) have been grown. The amino acid sarcosine is an isomer of the protein amino acid alanine. Both amino acids are described by the same chemical formula but have different structures; or, more specifically, in contrast to the alanine molecule, the sarcosine molecule has a symmetric structure. It has been found that the sarcosine phosphite compound undergoes a structural phase transition at a temperature of approximately 200 K. This result has demonstrated that compounds of achiral amino acids are more susceptible to structural phase transitions.     

Dielectric properties of betaine phosphite films

Polycrystalline films of betaine phosphite are grown on single-crystal quartz and lithium niobate substrates atop interdigitated transducers. It is revealed using a light-polarizing microscope in the reflection mode that the films are made up of large (up to 1 mm in size) single-crystal blocks. The temperature dependences of the film capacitance measured at frequencies from 120 Hz to 1 MHz pass through a strong maximum at the ferroelectric phase transition point. The effect of a bias on the permittivity of the films is investigated. It is shown that the differences in the temperature dependences of the permittivity of single crystals and films originate from the influence of dynamic strains in the substrate on the film and from the presence of an effective depolarizing field. Original Russian Text ? E.V. Balashova, B.B. Krichevtsov, V.V. Lemanov, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 3, pp. 525–532.     

Pyroelectric,piezoelectric, and polarization responses of glycine phosphite crystals with an admixture of glycine phosphate

Temperature dependences of the pyroelectric, piezoelectric, and polarization responses of glycine phosphite crystals containing different amounts of glycine phosphate were studied in the range 120–320 K. The experimental data obtained suggest the presence of a built-in bias field oriented along the twofold symmetry axis in these crystals. This field was found to be 5 kV/cm. It is suggested that the built-in bias plays a decisive role in the formation of the pyroelectric and piezoelectric crystal responses in the temperature interval 225–280 K, which is significantly higher than the ferroelectric phase transition point in nominally pure glycine phosphite crystals (224 K).     

Dielectric properties of betaine arsenate crystal near the phase transition

Dielectric measurements for single crystal of betaine arsenate (CH₃)₃NCH₂COO·H₃AsO₄ connected with the ferroelectric phase transition at 119 K were performed. The temperature dependence of electric permittivity was measured at dc electric fields up to 700 kV/m. The results show significant suppression of the dielectric constant by the application of dc field. Deviation from the classical behavior was observed. The electric permittivity was also measured in the paraelectric phase at constant temperature as a function of electric field intensity up to 700 kV/m. The electric permittivity might be well described by the classical relation with additional term including contribution to permittivity coming from clusters. The fit parameters indicate that the polar-clusters carries polarization P₀=0.7- with the clusters size of L=12-20 nm.     

Dielectric and ultrasonic investigation of phase transition in cuinp2s6 crystals

Investigation results of dielectric and ultrasonic properties of layered CuInP₂S₆ crystals are presented. At low frequencies, dielectric spectra are highly influenced by the high ionic conductivity with the activation energy of 7357.4?K (0.635?eV). The high-frequency part of the spectra is determined by relaxational soft mode. The critical slowing down and Debye-type dispersion show the order–disorder type of the phase transition. The temperature dependence of the relaxational soft mode and dielectric contribution show a quasi-one-dimensional behaviour. Ultrasonic velocity exhibits critical slowing down which is accompanied by attenuation peaks in the phase transition region. Layered CuInP₂S₆ crystals have extremely large elastic nonlinearity in the direction perpendicular to layers. The nonlinear elastic parameters substantially increases at the PT temperature.     

Dielectric permittivity in the smectic a phase of liquid crystals

We propose a functional dependence of the dielectric constant with the smectic order parameter of liquid crystals in their smectic A phase. The proposal is verified by comparing with the published values of heptylazoxybenzene.     

Dielectric properties of betaine phosphite-betaine phosphate solid-solution crystals in the improper ferroelastic phase

Temperature dependences of dielectric permittivity in the improper ferroelastic phase, including the region of the improper ferroelastic phase transition occurring at T=T_c1, were studied in the betaine phosphite-betaine phosphate solid-solution crystals. At a betaine phosphate (BP) concentration of 10%, the phase transition temperature T_c1 was found to shift toward higher temperatures by about 5 K compared to betaine phosphite (BPI) crystals, where T_c1=355 K. The phase transition remains in the vicinity of the tricritical point. As the BP concentration in BPI is increased, the dielectric anomaly at T=T_c1 weakens substantially compared to pure BPI. The nonlinear temperature dependence of reciprocal dielectric permittivity in the improper ferroelastic phase of BPI_xBP_1?x crystals is described in the concentration region 0.9≤x≤1 in terms of a thermodynamic model taking into account the biquadratic relation of the nonpolar order parameter of the improper ferroelastic phase transition to polarization. The decrease in the ferroelectric phase transition temperature T_c1 (or in the temperature of loss of improper ferroelastic phase stability) with increasing BP concentration in the above limits is due to the decreasing effect of the nonpolar mode on the polar instability, which is accompanied by a weakening of the dielectric anomaly at T=T_c1     

Anomalous properties of crystals with ferroelectric phase transition induced by off-center ions

It is given the theoretical study of some properties of strongly polarizable dielectric crystals in which off-center impurity ions induce ferroelectric phase transition. The spontaneous polarization, transition temperature, soft mode frequency, dielectric susceptibility, ultrasonic attenuation, nuclear spin-lattice relaxation are analyzed. The theory explains observed in K_1?xLi_xTaO₃ saturation of remanent polarization with off-center Li⁺ concentration increasing, close to $\text{x}$ dependence of phase transition temperature, the anisotropy of ultrasonic attenuation, the absence of anomalies of Li nuclear spin-lattice relaxation rate near T_c.     

Dielectric study of the liquid-solid phase transition in benzene

The liquid-solid phase transition in benzene is studied dielectrically. A resolution of the (p, ?/?^O) isotherm into a branch for the liquid and one for the solid is achieved. This result is similar to those obtained for the (p, V^O/V) isotherm in computer experimentals applying the rigid sphere model for the liquid.     

Ferroelectric films of deuterated glycine phosphite: Structure and dielectric properties

Polycrystalline textured films of deuterated glycine phosphite consisting of single-crystal blocks with lateral dimensions ～(50–100) μm and a thickness d ～ (1–5) μm have been grown by evaporation on NdGaO₃(100) and α-Al₂O₃ substrates with preliminarily deposited interdigitated electrodes, as well as on Al substrates. The c* (Z) crystallographic axis in the blocks is normal to the film plane, and the a (X) axis and the polar axis b (Y) are oriented in the film plane. The temperature dependences of the capacitance of the structures measured with the interdigitated electrode system reveal a strong dielectric anomaly at the film transition to the ferroelectric state. The phase transition temperature T _c depends on the degree of deuteration D of the glycine phosphite. The maximum value T _c = 275 K obtained in the structures studied corresponds to a degree of deuteration of the glycine phosphite D ～ 50%. The frequency behavior of the dielectric hysteresis loops in glycine phosphite films differs radically from that of the previously studied films of deuterated betaine phosphite, which evidences that polarization switching in these structures proceeds by different mechanisms. It has been that application of a dc bias to the electrodes changes the shape of the dielectric hysteresis loops and shifts them along the electric field axis. The shift of the loops depends on the sign, magnitude, and time of application of the bias. Possible mechanisms underlying the induced unipolarity are discussed.     

Dielectric properties of nickel-doped NaCl crystals

The influence of nickel impurities upon dielectric losses in natrium chloride crystals is studied. Experiments have shown that in non-heated samples, stored over prolonged periods of time, the majority of nickel is present in the form of aggregates and higher complexes. Their decomposition and the building up of dipoles depends in the first instance on sample heating and cooling methods. The aggregation of dipoles in time at room temperature is studied.It is shown that with nickel concentrations reaching approximately up to 2. 10^–3 mol% in heated and quickly cooled samples, all nickel builds itself into the NaCl lattice substitutionally in the form of dipoles Ni²⁺ + cation vacancy, while at higher concentrations some nickel precipitates or builds itself in in another non-substitutional way.The author wishes to express his thanks to Dr. Funk for making the polarographic analysis of the samples and to Dr. Bohun for valuable discussions of the results obtained.     

Dielectric properties of RbCl-RbBr mixed crystals

A systematic measurement of dielectric constant and loss on RbCl-RbBr mixed crystals in various compositions has been carried out in the frequency range 100 Hz to 100 kHz and in the temperature range from room temperature to 320°C. From these measurements the static dielectric constant, the Szigeti charge, the conductivity and the activation energy for conduction are evaluated. All these properties show a nonlinear composition dependence. Semiempirical equations proposed earlier are employed to evaluate the dielectric constant as a function of composition. The validity of these relations is also discussed.     

Acoustic properties of betaine phosphite in the vicinity of phase transitions

A study is reported of acoustic anomalies in the vicinity of the antiferrodistortive and ferroelectric phase transitions in nominally pure betaine phosphite crystals and a crystal with 3% betaine phosphate impurity. The observed anomalies in the velocity and damping rate of longitudinal acoustic waves propagating along different crystallographic axes are interpreted within Landau theory. It is shown that the phase transitions in these crystals are characterized by a relatively weak correlation of the order parameter to strain and by a considerable contribution to the acoustic anomalies of an interaction higher in order than striction. Fiz. Tverd. Tela (St. Petersburg) 40, 1090–1096 (June 1998)