Theoretical study of lattice stability and selective doping effects of V 4+ and Tb 4+ in the ZrGeO 4 lattice

Abstract

A theoretical study on lattice stability and local geometry distortions produced by the presence of V 4+ and Tb 4+ ions in a ZrGeO 4 lattice has been carried out by means of the ab initio perturbed ion method. Slater type orbitals for representing atomic centers and large clusters ranging from 122 to 135 atoms have been used. The energy required to substitute Zr 4+ or Ge 4+ for V 4+ is similar in spite of the negative defect reaction energy calculated for V 4+ entering into the dodecahedral site. The Tb 4+ doping into the eightfold coordinated site requires hafl the energy needed for Tb 4+ entering into the tetrahedral site. Positive defect reaction energies have been calculated for the substitution of Zr 4+ or Ge 4+ for Tb 4+. The doping process produces a decrease of force constant and vibrational frequency values associated with the approximate breathing normal vibrational mode for the two host sites.