AGEING OF THE DIELECTRIC CONSTANT IN (Hf, Zr)-DOPED BT CERAMICS

摘要: Ferroelectric properties of 9% mol (Hf, Zr)–doped BaTiO3 ceramics were studied, by comparison with those of pure tetragonal BaTiO3 ceramics. The addition of dopants lead to an increasing of the rhombohedral–to–orthorhombic and orthorhombic–to–tetragonal transition temperatures above 0 C and a decreasing of tetragonal–to–cubic (ferroelectric–to–paraelectric) transition temperature from 122 C to 95 C at heating and from 120 C to 85 C at cooling. At room temperature, the ageing process develops following two different mechanisms: a thermally activated ageing process in pure tetragonal ceramics leading to a linear dependence of the relative dielectric constant and dielectric losses upon logarithm of time. In doped BT ceramics, a defects diffusion process leading to a decreasing reversed-S curve of relative variation of capacity and tanδ upon logarithm of time could be observed. We considered that the main reason for the different ageing mechanisms is the crystalline symmetry, which influences the twinning process and the domain-wall dynamics. Our results prove that ageing of (Hf, Zr)-doped BaTiO3 ceramics depends on temperature by intermediate of the phase symmetry, which imposes the twinning rate and rearrangement of ferroelectric domains minimising the elastic energy of the lattice.