HoB4 at high pressure and low temperature: an experimental and theoretical study

Single crystals of HoB4 have been grown and used for synchrotron X-ray diffraction studies at pressures up to 23 GPa and temperatures down to 100 K. The experimental bulk modulus 195±6 GPa is in good agreement with 188.4 and 198.2 GPa values calculated in the LSDA and LSDA+U approximations, indicating that mainly the boron sublattice determines the bulk modulus. The experimental c/a ratio decreases slightly with pressure, but the effect is small. An orthorhombic distortion begins at T c≈ 295 K, i.e. at a temperature much higher than the Neel temperature T N1=7.1 K. The behavior is interpreted in terms of built-in strains and crystal mosaicity.