EPR line broadening in the ferroelectric phase induced by dipole impurities (KTa1-xNbxO3:Fe3+)

Measurements of angular and temperature dependences of EPR line broadening of Fe3+ axial centre in KTa1-xNbxO3 (x=0.06) are carried out within 77-4.2 K temperature range. It is shown that the whole line broadening at T=4.2 K is caused both by unresolved decomposition resulting from occurrence of spontaneous polarization and by broadening of individual components due to the presence of polarization space fluctuations in KTaO3:Nb impurity ferroelectric. Value of noncentral shift of Nb x0 ≅ 5x10-2 - 3x10-3 A ions is estimated using point ion model and theory of EPR line electrodipole breaking in ferroelectric in the assumption that Nb ions are noncentral ones in paraelectric phase