HIGH-PRESSURE STUDIES ON YNI2B2C AT ROOM-TEMPERATURE

The electronic and lattice structure, and equation of state behavior o f YNi2B2C has been investigated by electrical resistivity, thermoelect ric power, and angle-dispersive x-ray-diffraction measurements. The el ectrical resistance under pressure has also been measured for other la nthanide-nickel borocarbides (RNi2B2C, R=Ho, Er, and Tm). The high pre ssure behavior is analyzed by electronic band-structure [tight-binding linear muffin-tin orbital (LMTO) and full-potential LMTO] calculation s on YNi2B2C. The measured thermoelectric power shows a peak around 2 GPa pressure. X-ray powder diffraction measurements of the lattice par ameter under pressure reveal that the carbon-filled variant of ThCr2Si 2-type tetragonal structure prevailing under ambient conditions is pre served in YNi2B2C up to 6 GPa. Pressure-volume data on YNi2B2C yielded a bulk modulus of 200 GPa. This is in agreement with the value comput ed by the first-principles electronic-structure calculations. It is al so shown that the observed peak in the thermoelectric power in YNi2B2C and the weak pressure dependence of the superconducting-transition te mperature can be correlated with the details of the electronic density of states.