Calculation of Debye temperature for crystalline structures - A case studyon Ti, Zr, and Hf

The methods to calculate the Debye temperature from elastic moduli have bee n reviewed. The approximation approach due to Moruzzi e al was critically e xamined by considering experimental elastic constant data for all the cubic elements. It was found that many cubic elements are exceptions with regard to the assumed constant scaling factor for the expression of the average s ound velocity in terms of the bulk modulus, and consequently the Debye temp erature of a cubic element must be calculated from the knowledge of all the elastic constants of the system. On the other hand, a fairly constant scal ing factor has been found to exist fur the hexagonal elements. Through the study of experimental data, some empirical relationships have been observed between the high temperature entropy-Debye temperature theta (D)(0) and th e low temperature limit of the Debye temperature theta (D)(-3). For those s tructures that are dynamically unstable at low temperatures, we proposed a way to obtain their theta (D)(0) from the calculated isotropic bulk moduli. The methods have been applied to calculate the Debye temperatures of hcp, bcc, and fee Ti, Zr, and Hf from their elastic moduli derived from ah initi o calculations. The calculated results agree very well with the experimenta l data. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. Al l rights reserved.