THERMODYNAMICS OF IMPURE ANHARMONIC CRYSTALS

The vibrational thermodynamic properties of doped anharmonic solids ar e investigated using thermodynamic Green's functions. The study uses c ubic and quartic anharmonic interactions, and different masses and for ce constants for the impurity and host lattice atoms. The explicit exp ressions so derived for the partition function, free energy, entropy, and lattice heat capacity for these solids in the low-impurity-concent ration limit are discussed for various situations. Our results are mod ified due to the presence of interaction terms between the anharmonic and localized fields and reduce to those obtained by earlier workers a s limiting cases.