Preparation, structural characterization and ferroelectric properties of compensated Te-doped n=2 Aurivillius oxides ceramics

New solid solutions Bi2-xTexSrNb2-xBxOy (B = Zr, Hf; 0 less than or equal to x less than or equal to 0.5) and Bi(2-y)Te(y)Sr(1-y)A(y)Nb(2)O(9) (A = K; 0 less than or equal to y less than or equal to 0.25) have been synthesized and characterized by powder X-ray diffraction methods, thermal analysis and dielectric measurements. Evolution of the unit-cell parameters at room temperature shows that doping the A or B perovskite sites dominates the size of (001) plane in the structure, whereas the c value is largely influenced by the cations which occupy the bismuth position in its layer. Thermogravimetric studies show that these materials are stable up to 800 degrees C for x, y = 0.25 and 750 degrees C for x = 0.5. Differential thermal analysis curves of x = 0.25 compounds exhibit one exothermic peak at 400 and 500 degrees C fur zirconium and hafnium phases, respectively. This effect is related to the expansion of their network, without changing the symmetry or space group. All compositions are ferroelectric at room temperature, and exhibit a non-zero d(33) value after poling. Measurements of the dielectric permittivity as a function of the temperature reveal signs of at least two possible phase transitions. The disappearance of the induced spontaneous polarization when heating samples above the lower temperature anomaly in the dielectric permittivity clarifies the T-c value of the compounds. Assuming they are displacive-type ferroelectrics, it can be shown that the variation of T-c with the composition is an effect of the change of the unit cell size. This result offers the possibility of tailoring a ferroelectric material with the desired thermal working range. (C) 2000 Elsevier Science Ltd. All rights reserved.