Phase transitions in crystals of protein amino acids with trapped drops of water solutions

It has been shown that the phase transitions observed at temperatures of about 250 K in crystals of protein amino acids and of their compounds grown from water solutions are related to drops of these solutions trapped by crystals in their growth.     

A study of the structural phase transition in strontium titanate single crystal by coherent and incoherent second optical harmonic generation

The surface phase transition in a SrTiO₃ crystal was studied by second optical harmonic generation. Nonlinear optical response singularities were observed at temperature T*=145 K, which was 40 K higher than the T_c structural phase transition temperature in the crystal volume. Nonlinear critical opalescence in the crystal volume caused by the presence of point defects was studied. The second harmonic field and the intensity of critical opalescence were calculated based on the phenomenological model of nonlinear optical processes with the use of the Landau theory of phase transitions.     

Polar phonons and specific features of the ferroelectric states in cadmium titanate

Polarized spectra of reflectance R(ν) and transmittance Tr(ν) of single-crystal CdTiO₃ samples have been obtained in the frequency range 7 < ν < 1000 cm^?1 and for temperatures from 5 to 300 K using IR Fourier spectroscopy and submillimeter-range techniques. Dispersion analysis was carried out in terms of the additive-oscillator model, and dielectric responses ε(ν) and ε″(ν) were calculated. The polar modes were assigned to particular symmetry types, and their oscillator parameters (dielectric contributions, normal frequencies, damping constants) were determined. The numerical values of the components of the static permittivity tensor, ε₁₁ and ε₃₃, are shown to be almost fully determined by the total dielectric contributions due to the B_3u and B_1u phonons, respectively. In the low-frequency domain, lines showing anomalous behavior of the oscillator parameters, which is characteristic of soft ferroelectric modes, were observed. It is shown that, in CdTiO₃ at cryogenic temperatures, there exist several different polar states with switching in the direction of the spontaneous polarization vector.     

Phase transitions in crystals of protein amino acids

The temperature dependence of the piezoelectric response of many protein amino acids and their compounds exhibits a sharp increase in the piezoelectric response signals at a certain temperature. It has been shown using the example of the known ferroelectrics without a piezoelectric effect in the paraphase (triglycine sulfate, glycine phosphite, trisarcosine calcium chloride) that such an increase in the piezoelectric response is associated with the structural phase transition to the low-symmetry piezoelectric phase with a large number of piezoelectric coefficients. The specific features of the phase transitions with the symmetry change D ₂-C ₂ have been discussed.     

Unusual electromechanical effects in glycine

Unusual piezoresponse signals have been observed in glycine aminoacid powder at a frequency near 10 MHz, which exhibited a regular pattern in time determined by a periodic phase variation in the elastic vibrations of individual powder particles. This phenomenon results from the formation of spatial structures in glycine powder under the action of a strong rf field. Fiz. Tverd. Tela (St. Petersburg) 40, 1086–1089 (June 1998)     

Effect of electric field on the dielectric permittivity of betaine phosphite crystals in the paraelectric phase

Temperature dependences of the dielectric permittivity of betaine phosphite crystals are studied both without and under application of an electric bias. It is shown that, in view of the fact that the high-temperature improper ferroelastic (antiferrodistorsive) phase transition at T _c1=355 K is nearly tricritical, the nonlinear temperature dependence of inverse dielectric permittivity in the paraelectric phase and the effect of the field on the dielectric permittivity can be described within a phenomenological model containing two coupled (polar and nonpolar) order parameters with a negative coupling coefficient. An analysis of the model revealed that, in the case where two phase transitions, a nonpolar and a ferroelectric one, can occur in the crystal, all of its dielectric properties, including the polarization response in a field, can be described by one dimensionless parameter a. For the crystal under study, we have a=?2.5. This value of the parameter corresponds to a second-order ferroelectric transition far from the tricritical point, at which a=?1. It is shown that the polarization response in the paraelectric phase in an electric field calculated within this model differs radically from that in the ferroelectric phase-transition model for which the Curie-Weiss law holds in the paraelectric phase.     

Raman spectra of cadmium titanate

Polarized Raman spectra of CdTiO₃ single crystals are recorded for the first time over the frequency range 5 < ν < 1000 cm^?1 at temperatures of 10 to 1200 K. The emphasis was on the low-frequency range, where an anomalous temperature dependence of a few phonon modes was observed. At high temperatures, four phonon modes exhibiting a behavior typical of soft modes were found to exist. These phonon modes are assumed to restore the cubic symmetry of the lattice. Their extrapolated temperature dependences suggest that there exists a sequence of three hypothetical high-temperature phase transitions analogous to those observed in the genuine perovskite CaTiO₃. At temperatures below 78 K, the Raman spectrum exhibits new lines associated with polar distortions of the unit cell. At low frequencies, three lines are observed whose parameters exhibit an anomalous behavior typical of soft modes in a ferroelectric phase. Several different polar states are assumed to exist at low temperatures.     

Phonon echo in L-alanine

Phonon echo signals have been observed in a finely-dispersed crystalline powder of the L-alanine amino acid. Measurements of the relaxation time T ₂ have revealed a phase transition in L-alanine crystals at a temperature of about 170 K. Fiz. Tverd. Tela (St. Petersburg) 40, 2119–2120 (November 1998)     

Experimental studies of the thermal properties of thin films by a probe technique with periodic heating

The thermal properties of SrTiO₃ thin films are investigated experimentally by recording the amplitude and phase of the temperature oscillations of a flat probe with the heat flux perpendicular to the plane of the film. Results are given from measurements of the specific heat and thermal conductivity of a leucosapphire substrate and the thermal conductivity of a SrTiO₃ film of thickness 2 μm. Fiz. Tverd. Tela (St. Petersburg) 39, 1299–1302 (July 1997)