4-CONSTANT POTENTIAL FUNCTION OF AMORPHOUS SELENIUM AND EVALUATION OFITS THERMODYNAMIC AND ACOUSTIC PROPERTIES

Litov and Anderson after various considerations suggested a four const ant potential function for a-Se as well as a-As2S3. Hence we also used a four constant potential function with the sole purpose of applying this potential function to obtain several acoustic, thermodynamic and other properties. We calculated several acoustic properties of a-Se li ke second order elastic constants (SOECs), their pressure derivatives, the longitudinal and transverse Gruneisen constant by two different m ethods, phonon frequencies, absorption band position through the use o f Nath-Smith-Delaunay's equation, and the thermodynamic properties lik e heat capacity, bulk modulus, thermal Gruneisen constant, the pressur e derivative of the bulk modulus (dK(T)/dP = C-1), the pressure deriva tive of C-1 which is related to Anderson-Gruneisen parameter, pressure derivative of Gruneisen constant namely gamma(g)' which is related to second Gruneisen constant, characteristics of phonon frequencies, pot ential energy function through the use of fitted parameters and third order elastic constants. Finally we calculated K-T at the reduced dens ity of rho/rho(0) = 1.1. K-T is Obtained from the potential function w ith the fitted parameters. In all the above cases the calculated value s are found to be in good agreement with experiment wherever available . In this connection it is important to point out that we eliminated ' C' a constant in the potential function using the equilibrium conditio n as was done by Litov et al in a-Se and Gerlich er al in the case of a-As2S3 as all amorphous substances are isotropic as mentioned by seve ral authors. We contemplate to calculate several other properties for a-Se and a-As2S3 and present them at a later stage.