tailieunhanh - High-pressure EXAFS Debye-Waller Factors of Metals

The anharmonic correlated Debye model has been developed to investigate the pressure effects on the extended X-ray absorption fine structure (EXAFS) Debye-Waller factors of metals. The recent well-established Grüneisen parameter expressions have been applied to formulate the pressure-dependent analytical expressions of the effective spring constant, correlated Debye frequency and temperature. | VNU Journal of Science: Mathematics – Physics, Vol. 33, No. 1 (2017) 76-80 High-pressure EXAFS Debye-Waller Factors of Metals Nguyen Viet Tuyen1, Tran Thi Hai2, Nguyen Thi Hong2, Phan Thi Thanh Hong3, Ho Khac Hieu4,* 1 VNU University of Science, 334 Nguyen Trai, Hanoi, Vietnam 2 Hong Duc University, Thanh Hoa, Vietnam 3 Hanoi Pedagogical University No 2, Vinh Phuc, Vietnam 4 Duy Tan University, Da Nang, Vietnam Received 05 December 2017 Revised 16 February 2017; Accepted 20 March 2017 Abstract: The anharmonic correlated Debye model has been developed to investigate the pressure effects on the extended X-ray absorption fine structure (EXAFS) Debye-Waller factors of metals. The recent well-established Grüneisen parameter expressions have been applied to formulate the pressure-dependent analytical expressions of the effective spring constant, correlated Debye frequency and temperature. Combing with the anharmonic correlated Debye model, the expression of EXAFS Debye–Waller factor under pressure can be derived. Numerical calculations, performed for Fe and Cu metals show reasonable agreement with experiments. Keywords:EXAFS, Debye-Waller factors, Debye model, Anharmonicity, Pressure 1. Introduction One of the most effective methods for investigation the structure and thermodynamic properties of crystals is extended X-ray absorption fine structure (EXAFS) [1]. The anharmonic EXAFS provides information on structural and thermodynamic properties of substances. The EXAFS oscillation has been 2 analyzed by means of cumulant expansion approach containing the second cumulant σ2 σ which is an important factor in EXAFS analysis since the thermal lattice vibrations affect sensitively on the XAFS amplitudes through the factor exp 2σ 2k 2 . The second cumulant corresponds to the parallel mean square relative displacement or Debye-Waller factor (DWF). The EXAFS is sensitive to temperature and pressure [2] which can make changes of cumulants including DWF, which in turn lead