High-pressure studies on YNi(2)B(2)C at room temperature

Abstract

The electronic and lattice structure, and equation of state behavior of YNi(2)B(2)C has been investigated by electrical resistivity, thermoelectric power, and angle-dispersive x-ray-diffraction measurements. The electrical resistance under pressure has also been measured for other lanthanide-nickel borocarbides (RNi(2)B(2)C, R=Ho, Er, and Tm). The high pressure behavior is analyzed by electronic band-structure [tight-binding linear muffin-tin orbital (LMTO) and full-potential LMTO] calculations on YNi(2)B(2)C. The measured thermoelectric power shows a peak around 2 GPa pressure. X-ray powder diffraction measurements of the lattice parameter under pressure reveal that the carbon-filled variant of ThCr(2)Si(2)-type tetragonal structure prevailing under ambient conditions is preserved in YNi(2)B(2)C up to 6 GPa. Pressure-volume data on YNi(2)B(2)C yielded a bulk modulus of 200 GPa. This is in agreement with the value computed by the first-principles electronic-structure calculations. It is also shown that the observed peak in the thermoelectric power in YNi(2)B(2)C and the weak pressure dependence of the superconducting-transition temperature can be correlated with the details of the electronic density of states.