Characteristics of the Thermodynamic and Kinetic Properties
of NbH_0.83 in the Phase Transition Region

N. A. Sorokina*, D. Wlosewicz**, T. Plackowski**, H. Misiorek**, and Ch. Sulkowski**

* Institute of High-Pressure Physics, Russian Academy of Sciences, Troitsk, Moscow oblast, 142092 Russia

** Institute of Low Temperature and Structure Research, Polish Academy of Sciences,
P.O. Box 937, 50-950 Wroclaw, Poland

Received February 25, 2000

Abstract—Measurements were made of the specific heat (in the temperature range 80–400 K), electrical resis-
tivity (4.2–300 K), thermo-emf (4.2–300 K), thermal conductivity (7–300 K), magnetic susceptibility (4.2–400 K),
and lattice parameters (30–300 K) of the alloy NbH_0.83. The ' phase transitions were studied. It
was established that the structure of the niobium matrix of the hydride remains unchanged as a result of these
transitions. It is shown that the phase transition (one-dimensional hydrogen ordering) is a three-stage
one and is accompanied by a substantial change in the shear modulus of the hydride. The ' phase existing at
T< 110 K was determined. The electron thermal conductivity _el calculated for the ' phase in the range T <
23K is 25% higher than the measured thermal conductivity. In order to explain this fact and also the disconti-
nuity in the concentration dependence of the coefficient of thermal expansion of NbH_x for x 0.83–0.84 and
the approximately 1.5% compression of the NbH_0.84 volume it is assumed that in the region of x_c in the ' phase
the topology of the Fermi surface of the NbH_x interstitial alloy changes substantially. © 2000 MAIK
“Nauka/Interperiodica”.

Pleiades Publishing home page | journal home page | top

If you have any problems with this server, contact webmaster.