High-pressure studies on ${\mathrm{YNi}}_2{\mathrm{B}}_2$C at room temperature

The electronic and lattice structure, and equation of state behavior of ${\mathrm{YNi}}_2{\mathrm{B}}_2$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 $(R{\mathrm{Ni}}_2{\mathrm{B}}_2\mathrm{C},$ $R=\mathrm{Ho},$ 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 ${\mathrm{YNi}}_2{\mathrm{B}}_2\mathrm{C}.$ 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 ${\mathrm{ThCr}}_2{\mathrm{Si}}_2$-type tetragonal structure prevailing under ambient conditions is preserved in ${\mathrm{YNi}}_2{\mathrm{B}}_2\mathrm{C}$ up to 6 GPa. Pressure-volume data on ${\mathrm{YNi}}_2{\mathrm{B}}_2\mathrm{C}$ 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 ${\mathrm{YNi}}_2{\mathrm{B}}_2\mathrm{C}$ and the weak pressure dependence of the superconducting-transition temperature can be correlated with the details of the electronic density of states.