Open AccessPressure and temperature dependence of EXAFS Debye–Waller factors in diamond‐type and white‐tin‐type germanium
Author(s) -
Yoshiasa Akira,
Nagai Takaya,
Ohtaka Osamu,
Kamishima Osamu,
Shimomura Osamu
Publication year - 1999
Publication title -
journal of synchrotron radiation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.172
H-Index - 99
ISSN - 1600-5775
DOI - 10.1107/s0909049598011947
Subject(s) - extended x ray absorption fine structure , tin , diamond , diamond anvil cell , interatomic potential , germanium , synchrotron radiation , chemistry , x ray absorption fine structure , atom (system on chip) , bond length , analytical chemistry (journal) , materials science , absorption spectroscopy , diffraction , crystallography , crystal structure , molecular dynamics , spectroscopy , optics , silicon , computational chemistry , physics , organic chemistry , chromatography , quantum mechanics , computer science , embedded system
Extended X‐ray absorption fine‐structure (EXAFS) spectra near the Ge K ‐edge in diamond‐ and white‐tin‐type Ge under high temperature and high pressure were measured using a cubic‐anvil‐type apparatus (MAX90) with synchrotron radiation from the Photon Factory, Tsukuba, Japan. Pressure values up to 10.6 GPa were estimated on the basis of the isothermal equation of state of the diamond‐type Ge within an accuracy of 0.4 GPa. Pressures for the same cell assembly were also determined by X‐ray diffraction experiment using the NaCl scale. The diamond‐type Ge is of great advantage to the pressure calibrant of EXAFS measurements at elevated temperature because a harmonic approximation can be applied up to 900 K. By the phase transition from diamond‐ to white‐tin‐type phases, with an increase in coordination number, Ge—Ge distances increase. A sixfold‐coordinated Ge atom in the white‐tin‐type structure has crystallographically non‐equivalent two kinds of nearest‐neighbour distances [2.530 (8) Å and 2.697 (8) Å at 12.8 GPa]. The harmonic effective interatomic potential, V ( u ) = 1/2α u 2 , was evaluated from the contribution to the thermal vibration, where u is the deviation of the bond distance from the location of the potential minimum. The potential coefficient, α, at 0.1 MPa is essentially temperature independent and is 9.06 eV Å −2 . At 9 GPa the potential coefficient is 9.71 eV Å −2 . The effective interatomic potential is influenced not only by pressure but also by changes in coordination number. The high‐pressure white‐tin‐type phase has a broader potential and a relatively larger mean square amplitude of vibration than the diamond‐type phase.