Browsing by Author "Xu, JA"

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High-pressure phase transitions in Zn1-xMxSe (M=Cd, Fe, and Mn)
(1998-07-01)
Lin, CM
;
Chuu, DS
;
Xu, JA
;
Huang, E
;
Chou, WC
Energy-dispersive x-ray diffraction was employed to study pressure-induced phase transitions in Zn0.84Fe0.16Se, Zn0.9Cd0.1Se, and Zn0.76Mn0.24Se crystals up to 21.0, 23.3, and 24.3 GPa, respectively. Our result shows that the B3 to B1 structure transitions for these crystals occurred at 1 1.4 +/- 0.5, 9.5 +/- 0.3, and 9.6 +/- 0.5 GPa, respectively. Compared to the phase-transition pressure (P-t) of ZnSe (14.4 GPa), a reduction of about 3-5 GPa is exhibited in these ternary compounds. This reduction in phase-transition pressure Delta P-t in the ternary compounds suggests that the fractional volume change, (Delta V/V-o), of the B3-B1 phase admixture might be the source of this reduction. Our results indicate that P-t (with respect to the phase transition pressure 14.4 GPa of ZnSe) is related to the fractional volume change (Delta V/V-o) by the expression P-t = [14.4003 + 0.1568 (Delta V/V-o)-0.0281(Delta V/V-o)(2)] GPa. [S0163-1829(98)05426-5].
Phase transitions of Zn0.84Fe0.16Se under high-pressure
(1998)
Lin, CM
;
Chuu, DS
;
Chou, WC
;
Xu, JA
;
Huang, E
The energy-dispersive X-ray-diffraction (EDXD) and Raman spectroscopy were employed to study the pressure induced phase transitions of Zn0.84Fe0.16Se crystal up to 21.0 and 32.0 GPa, respectively. A semiconductor-metal transition was identified by EDXD and Raman spectroscopic methods at 11.4 +/- 0.5 GPa. Other two phase transitions were found only in the Raman scattering study below 11.4 GPa. In addition, three unidentified Raman peaks were still observable above the metallization pressure. The existence of Fe impurity in the ZnSe up to a concentration of 0.16 reduced prominently the semiconductor-metal phase transition pressure. For Raman works, the three unidentified Raman peaks of Zn0.84Fe0.16Se above 10.9 GPa are possibly the TO modes in the thin surface of the high pressure metallic phase. (C) 1998 Elsevier Science Ltd. All rights reserved.
Raman spectroscopy study of ZnSe and Zn0.84Fe0.16Se at high pressures
(1997-05-15)
Lin, CM
;
Chuu, DS
;
Yang, TJ
;
Chou, WC
;
Xu, JA
The ZnSe powder and Zn0.84Fe0.16Se crystal were studied by Raman scattering spectroscopy at pressures up to 36.0 and 32.0 GPa, respectively. For ZnSe powder at 4.7 and 9.1 GPa, two phase transitions were observed. However, the resulted phases have not been identified yet. As the pressure was increased to 14.4 GPa, the LO phonon peak disappeared while the TO phonon peak was still visible until the metallization pressure, 17.0 GPa was reached. In addition, three unidentified Raman peaks were still observable above the metallization pressure. For Zn0.84Fe0.16Se crystal, the structure transition from possible zinc blende to sodium chloride phase (B-1) was identified by the disappearance of Fe local mode and longitudinal optical (LO) phonon mode at 10.9 GPa. In addition, an unidentified phase transition at 4.7 GPa was observed. The TO phonon and the split TO phonons were still observable at a pressure above the phase transition pressure up to 32.0 GPa. The existence of Fe impurity in the ZnSe up to a concentration of 0.16 reduced the semiconductor-metal phase transition pressure to 10.9 GPa. According to the calculation of Gruneisen parameters, Zn0.84Fe0.16Se was found to have a higher ionicity than ZnSe. Reasons for the observation of Raman peaks at a pressure above the metallization pressure are still unknown.