Structure And Dielectric Properties Of Ln₃Fe₅O₁₂ Ceramics

In the present work,dielectric properties and ferroelectric properties of Y₃Al_xFe_5-xO₁₂(x=2,3),Y_1.5Bi_1.5Fe₅O₁₂ and Sm₃Al_xFe_5-xO₁₂(x=0,0.1,2) ceramics were investigated.The effects of composition and site occupations on the dielectric properties and the physical nature of the dielectric relaxations were discussed.Two dielectric relaxations of Y₃Al_xFe_5-xO₁₂(X=2,3) ceramics were identified in the temperature range from 125 to 573 K and in the frequency range from 1 Hz to 10 MHz.A Debye-type dielectric relaxation at low temperatures can be attributed to the charge carriers hopping between Fe²⁺ and Fe³⁺.The number of charge carriers decreases and the hopping distance between Fe²⁺ and Fe³⁺ increases with increasing the amount of Al³⁺,which results in the increase of the activation energy.The conduction contributes to the high temperature dielectric relaxation which has the similar activation energy of that of conduction.The charge carriers hopping related dielectric relaxation was not observed because the low sintering temperature and evaporation of Bi³⁺ significantly suppress the formation of Fe²⁺.The middle temperature dielectric relaxation with an activation energy of 0.70 eV most likely arises from the inhomogeneous structure,such as grain boundaries.The higher temperature dielectric relaxation also originates from the conduction.The P-E loop of Y_1.5Bi_1.5Fe₅O₁₂ ceramics was observed at room temperature.The lone pair electrons may contribute to the ferroelectricity of Y_1.5Bi_1.5Fe₅O₁₂ ceramics.Three dielectric relaxations of Sm₃Fe₅O₁₂ ceramics were observed in the temperature range from 125 to 573 K.The middle temperature dielectric relaxation and high temperature can be attributed to charge carriers hopping between Fe²⁺ and Fe³⁺ and conduction,respectively.Another dielectric relaxation at low temperatures with an activation energy of 0.22 eV is related to the 4f electrons of Sm³⁺.The increase of the amount of Al³⁺ weakens the low temperature dielectric relaxation.