We have carried out high-pressure X-ray structural studies of BeO and ZnO up to 200 GPa to find the phase transition of BeO from the wurzite to the NaCl structure and that of ZnO from the NaCl to the CsCl structure, which are expected theoretically. The phase transition of BeO occurred at 137 GPa, which is in good agreement with the theoretical value of 139 GPa. The wurzite phase persisted up to 175 GPa. The bulk modulus of BeO at zero pressure is determined to be 223 GPa by the Birch's equation. As previously reported, the ZnO sample transformed from the wurzite structure to the NaCl structure at 9.1 GPa. Extending the pressure range up to 202 GPa no phase transition to the CsCl structure occurred. The bulk modulus of the NaCl structure was determined to be 194 GPa.
. Ks, 64.70.Kb, 81.05.Dz High-pressure X-ray diffraction studies of Co x Zn 1-x O (x = 0, 0.05, 0.10) were carried out with a synchrotron radiation source. The crystal parameters for three samples under pressure were refined by the Rietveld method. The bulk moduli for Co x Zn 1-x O (x = 0, 0.05, 0.10) were determined by Birch's equation of state to be 144.9 ± 0.6, 143.4 ± 4.2, and 138.5 ± 1.9 GPa, and also the transition pressure from the wurtzite structure to the rocksalt structure were determined to be 8.2, 7.7, and 6.1 GPa, respectively. On increasing the Co-doping into the ZnO, both the bulk moduli and transition pressures decrease, but the rates are quite different. The bulk modulus decreases by 4.8% with 10% Co-doping but the transition pressure decreases by 25%.
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