Specific heat of KTiOPO4 within the 80–300 K range

The specific heat of the KTiOPO₄ crystal has been measured with a vacuum adiabatic calorimeter within the 80–300 K range. A peak-shaped anomaly in the specific heat indicating a phase transition has been revealed in the C _p (T) curve at T≅279 K. Numerical integration of smoothened experimental C _p (T) curves yielded the thermodynamic functions of KTiOPO₄, namely, the entropy, enthalpy, and reduced Gibbs energy. The entropy and enthalpy of the observed transition have been determined. Fiz. Tverd. Tela (St. Petersburg) 41, 497–498 (March 1999)     

Study of the heat capacity of Lu2Cu2O5 in the temperature range 366–992 K

Experimental data on the molar heat capacity of Lu₂Cu₂O₅ in the temperature range 366–992 K have been obtained. The experimental data have been used to calculate the thermodynamic properties of the oxide compound.     

Inelastic deformation of C60 single crystals in the temperature range 80–300 K

The rate spectrum of small inelastic strains of the C₆₀ single crystal in the temperature range 80–300 K has been obtained with a precision laser interferometer. It is revealed that the spectrum exhibits two large peaks in the glass formation (90–100 K) and phase transition (250–260 K) ranges. A small strain acceleration is also observed at ～220 and 240 K. The first two maxima are attributed to the changes in strain resistance upon transitions, and the strain acceleration at 220 and 240 K is associated with the annealing of the defects formed upon rapid cooling of the crystal. It is demonstrated that the peak at 250–260 K broadens with an increase in the stress. The spectrum of strain rates is compared with the calorimetric curve for the same single crystal.     

Heat capacity of high-purity isotope-enriched germanium-76 in the temperature range of 2–15 K

The heat capacity of high-purity isotopically-enriched germanium Ge-76 has been measured in the range of 2.5–15 K. In this range, the heat capacity of Ge-76 is 6–15% higher than the heat capacity of germanium of the natural isotopic composition, which is determined by a change in the average mass.     

Heat capacity of Tb2Cu2O5 in the temperature range 379–924 K

The heat capacity of Tb₂Cu₂O₅ in the temperature range 379–924 K has been measured using differential scanning calorimetry. It has been shown that the obtained dependence C _p = f(T) can be described by a combination of the Debye and Einstein functions.     

Pyroelectric properties of high-resistant KTiOPO4 crystals in the temperature range 4.2–300 K

The results of measuring the pyroelectric coefficient γ _s ^σ of nominally perfect KTiOPO₄ (KTP) crystals grown from solution in a melt with a potassium to phosphorus ratio of ～2 are presented. The γ _s ^σ (T) dependence is monotonic in the range from 4.2 to 250 K. Deviations from a linear dependence are observed beginning from 250 K, which is considered to be due to interstitial-potassium transport in the KTP crystal field. The spontaneous polarization of unclamped KTP samples is estimated from the results of the measurements. In terms of the crystal-physics approach, it is shown that the main contribution to a polar state of KTP is made by the dipole moments of two nonequivalent mesoscopic tetrahedra forming two sublattices that are polarized in opposite directions and bound by Ti(1) ions.     

Heat capacity of Tm2Cu2O5 in the temperature range 431–1004 K

The molar heat capacity of Tm₂Cu₂O₅ has been studied using differential scanning calorimetry in the temperature range 431–1004 K. The thermodynamic functions of the solid oxide compound have been calculated from the experimental data C _p = f(T).     

High-temperature heat capacity of YBiGeO5 and GdBiGeO5 in the range 373–1000 K

The oxide YBiGeO₅ and GdBiGeO₅ compounds have been synthesized by solid-phase synthesis. The high-temperature heat capacity has been measured using differential scanning calorimetry in the range 373–1000 K. The results were used to calculate the thermodynamic properties (the change in the enthalpy and entropy).

     

Effect of γ irradiation on the heat capacity of (CH3)2NH2Al(SO4)2 · 6H2O crystals near the ferroelectric phase transition

The heat capacity of dimethyl ammonium-aluminum sulfate crystals (DMAAS), both nonirradiated and γ-irradiated to fluences of 10⁷, 5×10⁷, and 10⁸ R, has been measured by the adiabatic method near the ferroelectric phase transition (PT) within the 80–300 K temperature range. The C _p =f(T) curve exhibits a λ-shaped anomaly near the phase-transition point T _C =152 K. The PT temperature and the magnitude of the anomaly are shown to decrease with increasing γ-irradiation fluence. It has been established that the ferroelectric PT at T _C =152 K, which lies close to the tricritical point, shifts progressively more under γ irradiation toward the second-order PT, and that the behavior of the anomalous part of the heat capacity in the ferroelectric phase is described by the thermodynamic theory of Landau. The experimental heat-capacity data have been used to calculate the variation of the thermodynamic functions of the DMAAS crystal.     

Electrically stimulated movement of edge dislocations in silicon in the temperature range 300–450 K

The movement of edge dislocations and the related acoustic emission of Si (111) carrying a direct current of density 0.5?5×10⁵ A/m² in the [110] direction are studied in the temperature range T=300–450 K. It is shown that the basic mechanism of dislocation movement is the electric wind determining the magnitude of the effective charge (per atom of the dislocation line) Z _eff=0.06 (n-Si) and ?0.01 (p-Si). Matching theory with experimental data has made it possible to determine the main contribution of edge dislocations to the acoustic-emission response of the silicon samples under investigation. The characteristic transition frequencies of dislocations in n-and p-Si from one metastable state into another are found to be f _max=0.1–0.5 Hz. The numerical values of the diffusion coefficient for atoms in the dislocation impurity atmosphere are estimated as 3.2×10^?18 m²/s (n-Si) and 1.5×10^?18 m²/s (p-Si).     

Specific features of the pyroelectric properties of actual RbTiOPO4 single crystals in the temperature range 4.2–300 K

The pyroelectric properties of samples cut from various growth sectors of RbTiOPO₄ single crystals grown from solution in a melt were measured in the temperature range from 4.2 to 300 K. The experimental values of the pyroelectric coefficient range from ?1.3 × 10^?5 to ?4.6 × 10^?5 C/m² K. For the samples cut from the (100) sector, pronounced anomalies were revealed at 85 and 275 K, which, in our opinion, can be due to the contribution of associates formed by the coordination tetrahedra PO₄(1) and PO₄(2) and interstitial rubidium Rb _i . At T > 280 K, superionic conductivity begins to manifest itself in all of the samples studied, which indicates the decomposition of the dipole complexes with increasing temperature. From the measured pyroelectric coefficient and birefringence along the polar direction, the spontaneous polarization of rubidium titanyl is calculated to be 0.5 C/m² at 250 K, which is comparable in magnitude to that of lithium tantalate.     

Creep behaviour of Zr + 4·5%Sn + 1%Mo in 300 K–750K temperature range

Measurements of the Young modulus normalized yield stress and the stress sensitivity parameter in creep of the Zr + 4·5% Sn + 1% Mo alloy in the temperature interval 300 K –750 K are presented. It is shown that there exists a plateau in the temperature dependence of the Young modulus normalized yield stress in the temperature range 540 K–660 K. The stress sensitivity parameter and the activation area exhibit a maximum at about 550 K. The discontinuous creep deformation is observed. It is suggested that the dynamic strain aging plays a significant role in the creep deformation of the Zr + 4·5% Sn + 1% Mo alloy in the temperature interval 540 K–660 K.This paper has been prepared for the Symposium Recent Problems in the Plasticity of Metals and Alloys, Prague, August 1980.The authors thank Prof. J. adek, DrSc., for valuable discusions.     

Evolution of the structure of Rb2ZnCl4 over the temperature range 4.2–310 K

X-ray diffraction is used to study the temperature dependence of the lattice parameters and the sequence of structural realignments in crystalline Rb₂ZnCl₄ over temperatures of 4.2–310 K. The appearance of and changes in the system of satellite reflexes indicative of structural ordering are studied. Below 74 K, on going into the monoclinic phase (space group A11a), anomalies are observed in the behavior of the lattice parameters, and superstructural reflexes develop with wave vectors q=a ^*/3+b ^*/2+c ^*/2 corresponding to an increase by a large factor in initial parameters a, b, and c of the Pnma-phase. Fiz. Tverd. Tela (St. Petersburg) 41, 1084–1090 (June 1999)     

Thermal conductivity of nitrogen in the temperature range 350–2500 K

The thermal conductivity of nitrogen is determined in a conductivity column instrument in the temperature range of 338 to 2518 K with an estimated uncertainty of about ± 1·5 per cent. The experimental data points are correlated by a cubic polynomial in temperature, viz. k(T)/(mW m^-1 K^-1) = 12·18 + 0·05224(T/K) - 0·6482 × 10^-6(T/K)² - 0·2765 × 10^-9(T/K)³. These conductivity values determined from heat transfer data taken in the continuum regime are found to be in fair agreement with the values obtained from similar data referring to low pressure range.

The present results are compared with the conductivity determinations of other workers and with the predictions of various theories developed for polyatomic gases. It is pointed out that a reliable calculation of thermal conductivity over an extended temperature range is impossible at the present time due to the absence of a large variety of experimental molecular data needed for such an effort. Average values of the vibrational energy diffusion coefficient, D _vib, are computed from the present k(T) data.     

Thermal conductivity of single-crystal ZrO2-Y2O3 solid solutions in the temperature range 50–300 K

The thermal conductivity of ZrO_2−x Y₂O₃ single crystals (x = 0.5, 1.5, 2.0, 2.5, 3.0, 8.0 mol %) has been studied experimentally in the temperature range 50–300 K. The influence of high-temperature annealings on the thermal conductivity has been analyzed.     

Heat capacity of YAl3(BO3)4 in the range of 329–1051 K

Single-crystalline YAl₃(BO₃)₄ is grown by spontaneous crystallization from a RAl₃(BO₃)₄-based solution-melt. The heat capacity in the temperature range of 329–1051 K is measured by differential scanning calorimetry. The thermodynamic functions of the YAl₃(BO₃)₄ solid compound are determined.     

An AC magnetic susceptibility bridge and cryostat for the temperature range 2–300 K

A mutual inductance bridge to measure low frequency magnetic susceptibilities of magnetic materials has been constructed. Salient features of the bridge, which uses a variable mutual inductance simulated using operational amplifiers, the cryostat and the coil assembly are described in this paper. The apparatus has been employed for accurate measurement of superconducting transition temperatures and for sensitive detection of magnetic ordering transitions in liquid helium and liquid nitrogen temperature ranges respectively. The bridge has been calibrated to determine the static susceptibility of magnetic materials as a function of temperature.     

Specific features of thermal resistance of silicon in the temperature range 105–130 K

Careful experimental investigations into the behavior of the thermal resistance of single-crystal silicon are carried out in the immediate vicinity of the temperature of an anharmonicity sign inversion (T _i =121.1 K), where phonon thermal resistance approaches zero. An anomalous positive deviation of the total thermal resistance (W) from the linear part of the temperature dependence with a maximum at 121.1 K is found in the temperature range 105–130 K. The temperature behavior of W in this range indicates that the mean free path of phonons is limited by a characteristic size of structural defects and that its temperature dependence exhibits specific features in the vicinity of T _i . It is established that the character of the temperature dependence of W above and below T _i is different. A linear functional relation between the total thermal resistance and the isobaric thermal strain is revealed at positive and negative anharmonicities of atomic vibrations.