The effects of iron as a dopant on the dielectric properties of ferroelectric potassium tantalate niobate (KTa_xNb_(1-x)O_3)

摘要

Presented here is a preliminary study on the effects of iron as a dopant in potassium tantalate niobate (KTa_xNb_(1-x)O_3) (KTN). Crystals of high purity were grown using a top-seeded isothermal method with starting materials that were purified ensuring that the impurity content was controlled down to less than 10 ppm. The study included introducing iron to KTN single crystals of high purity both during crystal growth and through thermal diffusion after growth. Dielectric measurements versus temperature were used to reveal the origins of the ferroelectric phase transition in the KTN:Fe system. Large shifts in the Curie temperature have been shown to be a direct consequence of the presence of iron impurities in KTN. The conventional theories of ferroelectricity do not explain this effect; however, a model is proposed to explain the observed behavior. The model is based on the concept of "polar microregions" proposed previously by Bidault and Maglione [J. Phys. I France 7, 543 (1997)] and others to explain ferroelectricity in potassium tantalate lightly doped with niobium.