X-Ray investigations of polycrystalline ethane in the temperature interval 6–90K have been performed. A previous suggestion that the structure of the orientationally ordered low-temperature phase III is monoclinic is confirmed, and the presence of an orthorhombic II and cubic I BCC phases near the melting temperature is also confirmed. It is shown that the intermediate phase II possesses a unit cell with the parameters a=4.289Å, b=5.660Å, and c=5.865Å. The volume jump ΔV at the III–II phase transition is found to be 0.21cm3∕mole (0.5%). It is suggested on the basis of the lack of reproducibility in the heating and cooling regimes that the phase II is metastable. It is determined that the volume change at the monoclinic-BCC phase transition in the interval 89.5–90K reaches ΔV=3.05cm3∕mole or 7.1%. The temperature dependences of the parameters and the volume of the low-temperature monoclinic phase III are studied for the first time. The linear and cubic thermal expansion coefficients are determined. It is found that the linear thermal expansion is anisotropic in the monoclinicity plane ac, increasing substantially as the phase transition temperature is approached. The specific heat of ethane at constant volume CV and the Gruneisen constant are calculated and the difference CP−CV is determined. It is shown that at temperatures above 50K CP−CV increases substantially as a result of an intensification of the rotational motion of the molecules.

The ultrasonic properties of La1−xCaxMnO3 (x ≈ 0.25) with the Curie temperature TC about 200 K are studied. Temperature dependences of longitudinal and transverse sound velocities were measured in zero magnetic field and for different constant magnetic fields as well. The ultrasonic study is supported by magnetic, resistive, magnetoresistive, structural and other measurements of the sample that facilitate interpretation of the results obtained. The magnetic field influence on sound properties found in this study presents some new features of the interplay between the elastic and magnetic properties of these compounds. It is shown that the paramagnetic-ferromagnetic transition in the sample studied is first order, but can become second order under the influence of applied magnetic field.

The structure and morphology of low-temperature quench condensed binary alloys of hydrogen with argon and krypton were studied by the powder x-ray diffraction. The nominal hydrogen fraction c in both systems was varied from 0 to 50%; the condensation was performed at 5-6 K; both as-prepared and annealed samples were examined by the x-ray diffraction. Few, often only one reflection can be unambiguously detected for the as-grown alloy samples. In the Kr-H 2 condensates with c < 10%, the x-ray patterns show fine-grain krypton-rich crystallites with rather high actual hydrogen contents as estimated from Vegard's law. At high nominal hydrogen fractions ( %) c ³ 10 , no the reflections attributable to the krypton lattice were recorded and the incoherent background showed no characteristic swelling around the position of reflection (111) from pure Kr but, instead, the reflections from a hydrogen-rich hcp phase were distinct. As the temperature was steadily raised, first the hydrogen reflections disappeared and then, at a certain temperature, the samples underwent an abrupt transformation, releasing heat and making the krypton component forms larger, x-ray detectable textured crystallites. In the as-grown Ar-H 2 samples, only (111) reflections from the argon-rich phase were recorded. Warmup led to the same consequences, viz., effusion of hydrogen and then recrystallization. In both systems, the recrystallization onset temperature depends substantially on the nominal hydrogen fraction in the gas. The shift of the lattice parameter in the as-grown argon-based phases suggests a strong suppression of the quantum nature of hydrogen in argon lattice environment. The entire set of the experimental findings can be treated as evidence that the quench-condensed hydrogen-containing alloys morphologically resemble helium-impurity solids (gels) whose structure and morphology are currently studied at Cornell University.