S. V. Stankus

Phase transitions and thermal properties of gadolinium trifluoride

Abstract The temperature dependence of gadolinium trifluoride density in the solid and liquid states was determined by a gamma attenuation technique. Volume changes on solid–solid and solid–liquid transitions were measured. The density and volume coefficient of thermal expansion of the liquid salt at the melting point are equal to 5609±25 kg m −3 and (16.2±0.5)×10 −5 K −1 , respectively. The relative density reduction on melting equals 16.7±0.15%. The polymorphic transformation from the low-temperature orthorhombic modification (a lattice of β-YF 3 type) into the high-temperature hexagonal phase (LaF 3 type) occurs with an increase of the density (about 2.1%). The peculiarities of the thermal expansion of the solid rare earth fluorides, undergoing phase transition β-YF 3 -type→LaF 3 -type, are discussed.

Study of the binary diffusion in liquid Sn–Pb and Al–Ge alloys by measurement of the melt concentration

Abstract A new method for the measurement of the coefficients of mutual diffusion in binary melts is described. The technique is based on immediate investigation of the evolution of composition profile with time in inhomogeneous liquid samples. The concentration is determined from measurement of the attenuation of the γ radiation in the melt. Diffusion factors of liquid alloys of tin–lead (50 at.% Pb) over the temperature range from 730 to 1030 K, and of aluminium–germanium (28.5 at.% Ge) at 1250 K were determined by this method. A comparison of the results obtained for the Sn–Pb system with literature data confirms the reliability of the proposed technique.

Electronic Phase Transition in Liquid Samarium

The irradiating of samples by a narrow beam of monochromatic gamma-rays with an energy of 662 keV is used to experimentally investigate the temperature and phase variations of the density of solid and liquid samarium (99.935%) in the temperature range from 293 to 1920 K. The results of measurements are presented in the form of tables. Density changes in structural transformations and melting are determined (1.70 ± 0.15%). The existence of a nonlinear dependence of the density of samarium in the liquid state is confirmed. Based on the obtained data and on the data available in the literature, a conclusion is made concerning the occurrence of electronic transformations in samarium during melting and thermal expansion in the liquid state.

Density changes of ytterbium trifluoride on phase transitions

Abstract The density and thermal expansion of the melt and high-temperature solid phase of YbF3 were studied by a gamma attenuation method. Volume changes on melting and on polymorphic transformation were measured. The density and volume coefficient of the thermal expansion of the liquid at the melting point are equal to 6284 kg m−3 and 14.7 × 10−5 K−1. Relative density changes on melting and on solid-solid transition are equal to 2.6% and 16.6%, respectively.

Anomalous transmission of gamma-rays of 0.662 MeV energy through single crystals of gallium garnets

Abstract It has been found experimentally that gamma-ray absorption (E γ =0.662 MeV ) in single crystals of Gd3Ga5O12 and Ca3(Nb,Ga)2Ga3O12 decreases at small angles between major crystallographic directions and beam direction. A magnitude of the effect is enhanced markedly as a temperature gradient perpendicular to the beam direction is created in the sample. The angular dependences of absorption coefficient look like orientation dependences observed at channeling of charged particles.

The calorific properties of LiYF4 : Nd in the solid and liquid states

The obtained experimental data are given in the figure and in Table 1. The enthalpy of solid LiYF4 : Nd was measured before and after the experiments in the liquid state. The agreement between the results of these measurement series proves the absence of an appreciable interaction between the melt and the ampoule material and that the calorific properties of polycrystalline LiYF 4 : Nd produced by rapid cooling and crystallization of the melt in the calorimeter do not differ from the properties of the initial single-crystal specimen. No systematic discrepancies were observed between the data obtained for different specimens.

Crystallization and thermal properties of rare earth gallium garnets

Abstract The density and thermal expansion of a number of rare earth gallium garnets were studied in the liquid and solid states in the regions of crystallization and melting by irradiating the samples with a narrow beam of gamma quanta. Volume changes on liquid-solid and solid-solid transitions were measured for equilibrium and nonequilibrium crystallization. The formulas for the estimation of the thermal properties of the liquid rare earth gallium garnets remaining to be explored were obtained.