XH DEFECTS IN NONMETALLIC SOLIDS - ISOTOPE EFFECTS AND ANHARMONICITIES AS PROBES OF THE DEFECT ENVIRONMENT

We have developed a technique to analyze the ir stretch modes of XH defects in nonmetallic solids, where X is an atom or ion heavier than hydrogen. This technique draws heavily upon molecular theory: The XH defect is treated by a Morse potential modified by coupling of X to the lattice with use of a one-dimensional model. The electrical anharmonicity of the dipole moment is included in obtaining transition strengths. The importance of overtone data as well as deuteration is demonstrated. A number of systems involving OH- in insulating solids are analyzed. These include (1) OH-, OD-, and OT- in TiO2 [J. B. Bates and R. A. Perkins, Phys. Rev. B 16, 3713 (1977)]; (2) OH- and OD- in Mg-doped LiF and NaF [R. Capelletti et al., Cryst. Latt. Defects Amorph. Mater. 16,189 (1987)]; (3) OH- and OD- in LiNbO3 [A. Forster et aL, Phys. Status Solidi B 143, 755 (1987)]; and (4) OH- and OD- in CsCl and CsBr [M. Krantz and F. Luty, Phys. Rev. B 37, 7038 (1988)]. The defects in TiO2 exhibit a surprisingly large mechanical anharmonicity. The data on Mg-doped fluorides indicate electrical anharmonicities which in some cases are considerably different from that of molecular OH-.