FERROELECTRIC THIN-FILMS WITH POLARIZATION GRADIENTS NORMAL TO THE GROWTH SURFACE

Thin film ferroelectrics with polarization gradients normal to the gro wth surface readily form when gradients in temperature, strain, or com position are coupled to the polarization vector in ferroelectric mater ials. This letter describes the formation of thin films of potassium t antalum niobate with graded polarizations obtained by grading the tant alum to niobium ratio of the ferroelectric phase. Unlike a simple stru cture consisting of laminated layers of ferroelectric material, the po larization gradient which forms breaks the natural symmetry of the fer roelectric material at any given plane, resulting in a self-poling of the structure subsequent to excitation by an oscillatory electric fiel d. Once poled, the devices reveal a measurable potential across the st ructure which varies with temperature. (C) 1995 American Institute of Physics.