Low-temperature properties of CePd2In

We report measurements of the specific heatC _p(T), electrical resistivity ϱ(T) and magnetic susceptibility ξ(T) of hexagonal CePd₂In, at low temperatures. Anomalies inC _p(T), χ(T) and ϱ(T) atT=1.23 K, indicate a phase transition, most likely to an antiferromagnetically-ordered phase. The electronic entropy reachesR ln2 per mole Ce at 9.2K, suggesting that the phase transition involves a doublet state. The ordered phase coexists with moderately correlated itinerant electrons.     

Influence of amorphization on the local environment and heat capacity of RNi<Subscript>5</Subscript> compound (<Emphasis Type="Italic">R</Emphasis> = La,Pr)

Heat capacity measurements of amorphous and crystallized R_16.7Ni_83.3 (RNi₅) samples (RNi₅) (R = La, Pr) in magnetic fields were performed, along with measurements of the average interatomic Ni–Ni distances and average square deviations from the interatomic distances. Changes were observed in the interatomic distances in La_16.7Ni_83.3, and in the electron component of the Pr_16.7Ni_83.3 heat capacity.     

Features of the local structure of rare-earth dodecaborides RB12 (R = Ho, Er, Tm, Yb, Lu)

The parameters of the local crystal structure of dodecaborides RB₁₂ (R = Ho, Er, Tm, Yb, Lu) have been determined by extended X-ray absorption fine structure (EXAFS) spectroscopy. It has been shown that the vibrations of the rare-earth ion with respect to the boron cage are well described in the harmonic approximation. At the same time, the displacement of rare-earth ions from equilibrium positions of the crystal structure should be taken into account to determine the length of the R-B bond. The analysis of EXAFS spectra has revealed the displacement of 1–6% of rare-earth ions by about 0.2–0.3 Å in all compounds under investigation; this displacement at low temperatures results in the formation of a cage glass phase.     

Local structure of nanopowders of refractory nitrides used to increase the critical current of high-temperature superconductors

The effect of dispersivity on the local-structure features in ZrN nanocrystals has been investigated by X-ray absorption (EXAFS) spectroscopy. The Debye-Waller factors and bond lengths have been determined for Zr-N and Zr-Zr coordination spheres. It is found that a decrease in the nanoparticle size leads to an increase in the static Debye-Waller factor for the Zr-Zr bond. The scale of changes is comparable with the increase in the Debye-Waller factor upon heating from 15 to 77 K.     

Local dynamic deformation of the superconducting CuO2 plane in the Nd2 − x Ce x CuO4 + δ compound

The local structure of the electron-doped high-temperature superconductor Nd_{2 ? x} Ce _x CuO_{4 + δ} has been investigated by EXAFS spectroscopy using synchrotron radiation in the temperature range 5–300 K. The radii, coordination numbers, and Debye-Waller factors of the nearest coordination spheres of the copper, neodymium, and cerium local environment have been obtained. The Einstein temperatures, characterizing the strength of Cu-O, Nd-O, and Ce-O interatomic bonds have been determined. The dynamic local deformation of the superconducting CuO₂ plane in the form of vibrations of some part of oxygen ions in a double-well potential due to the difference in the electronic filling of neighboring CuO₄ complexes has been established.     

The effect of water vapor on the electrical properties and sensitivity of thin-film gas sensors based on tin dioxide

The results of theoretical and experimental studies into the effect of water vapor on the electrical conductance of a gas sensor and the sensor response to hydrogen action are discussed. A relation describing the dependence of electrical conductance G₀ on absolute humidity in the pure air is derived using a hypothesis of the presence of space-charge regions depleted of electrons between the SnO ₂ grains in a polycrystalline tin dioxide film. Due to dissociative chemisorption of water molecules, the energy-band bending at the SnO ₂ grain interfaces decreases and the oxygen-vacancy concentration in the grains increases, resuling in an increase in G₀. An equation for the sensor response to hydrogen action is derived (the G₁/G₀, ratio, where G₁ is the sensor conductance in a gas mixture containing molecular hydrogen). The expression describes the dependence of G₁/G₀ on the hydrogen concentration in the interval 50–6·10³ ppm, band bending at the SnO ₂ grain interface, and sensor temperature. The dependences of the sensor conductance, highest possible conductance, and energy-band bending on temperature and absolute humidity resulting from processing of the experimental data are in good agreement with the theoretical predictions. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 50–56, August, 2008.