On the nature of ferroelectricity in Sr1−x A xTiO3 and KTa1−x NbxO3 solid solutions

摘要: Cluster calculations of the local adiabatic potential for an impurity atom in position A Sr1−xAxTiO3 (A=Mg, Ca, Ba, Pb, Cd, Zn), as well Nb and O atoms Ta-O-Nb chain KTa1−xNbxO3, were carried out nonempirical Hartree-Fock-Roothaan MO-LCAO formalism. For comparison, similar performed a sublattice-A ATiO3 cubic perovskites (A=Ca, Sr, Pb), K Ta KTaO3, Li K1−xLixTaO3. The revealed that all cases considered, except Zn, Mg, impurities, move single-well potentials corresponding solid solutions are displacive ferroelectrics. Zn Sr1−xZnxTiO3 Mg Sr1−xMgxTiO3 found to occupy off-center positions, does K1−xLixTaO3; i.e., they multiwell potential. An explanation is proposed first-order Raman scattering observed paraelectric phase above with central impurities. critical concentration xc KTa1−xNbxO3 was calculated virtual-crystal approximation within soft ferroelectric mode theory. values thus obtained agree available experimental data.