Browsing by Author "Chern, Yu-Ker"

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Pressure-Induced Phase Transitions in InAs Studied by Angular-Dispersive X-ray Diffraction and Raman Spectroscopy
(2015-06-01)
Lin, Chih-Ming
;
Lin, Kung-Liang
;
Chern, Yu-Ker
;
Lin, Yu-Kun
;
Chuang, Yu-Chun
Pressure-induced phase transitions in indium arsenide (In As) at ambient temperature were investigated by using angular-dispersive X-ray diffraction (ADXRD) and Raman scattering under high pressure up to around 9.8(1) and 9.9(2) GPa, respectively, with a 4:1 (in volume ratio) methanol-ethanol mixture as the pressure transmitting medium (PTM). In situ ADXRD measurements revealed that In As starts to transform from zinc blende (ZB) structure to rock-salt (RS) phase at 6.7(1) GPa, consistent with most previously reported studies. The phase transition proceeds steadily over a wide range of pressures and reaches completion at the highest applied pressure of 9.8 GPa with significant metallization, as suggested by the disappearance of Raman modes. In contrast to previous studies, our data did not show evidence of structural transition to Cnncm phase, presumably due to the different PTMs used and/or insufficient pressure applied. The order of appearance of the major diffraction peaks of RS phase In As with increasing pressure and intensity are explained by the binding energy density of the corresponding plane families. The zero-pressure isothermal bulk moduli (B-0) and its first-pressure derivatives (B-0\') for the ZB In As are 64(4) GPa and 3.8(2), respectively. The intensity of both the LO and TO phonon modes of ZB phase In As exhibits an abrupt decrease at 7.7(1) GPa, where equal weight fractions of ZB and RS phases are identified, suggesting the metallic nature of the RS phase.
Pressure-induced structural phase transition in bulk Zn0.98Mn0.02O by angular dispersive X-ray diffraction
(2014-08-15)
Lin, Chih-Ming
;
Lin, Kung-Liang
;
Chern, Yu-Ker
;
Hsu, Chia-Hung
;
Sheu, Hwo-Shuenn
The high pressure induced phase transition in bulk Zn0.98Mn0.02O at ambient temperature have been investigated using angular-dispersive X-ray diffraction (ADXRD) under high pressure up to around 13.80 GPa. For loading run, in situ ADXRD measurements found that a wurtzite-to-rocksalt structural phase transition pressure of bulk Zn0.98Mn0.02O began at 7.35 GPa. The fitting of volume compression data to the third-order Birch-Murnaghan equation of state yielded that the zero-pressure isothermal bulk moduli and the first-pressure derivatives were 157(8) GPa and 8(3) for the B4 phase, respectively. When decompress bulk Zn0.98Mn0.02O to ambient pressure a large part of the bulk Zn0.98Mn0.02O reverted to the B4 phase and only a small amount of the metastable B1 phase remained. We have exhibits the pressure dependence of lattice constant a and c axis, and the normalized ratio c/a of the bulk Zn0.98Mn0.02O. Possible pressure-induced phase transition mechanisms were explored by examining the cell parameters and the internal structural parameter (u) with pressures. The effect of the 3d electrons of manganese to increase the nearest-neighbor distance of O to Zn (Mn) parallel to the c axis may be the main reason for the phase transition of bulk Zn0.98Mn0.02O. An increase in the u value with pressure indicates that the B4-to-B1 phase transformation in bulk Zn0.98Mn0.02O is likely via the hexagonal path. (C) 2014 Elsevier B.V. All rights reserved.