Tham khảo tài liệu 'ferroelectrics material aspects part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 165 Performance Enhanced Complex Oxide Thin Films for Temperature stable Tunable Device Applications A Materials Design and Process Science Prospective Fig. 10. The theoretical average dielectric response as a function of temperature for three compositionally graded BarSri-rTiC 3 systems with the same nominal average composition. From Cole et al. 2007. Copyright 2007 American Institute of Physics. Electric Field kV cm Fig. 11. The temperature dependence of the dielectric tunability for the multilayered BST film from 90 to -10 C. The symbols on the plot represent the following temperatures 90 C open circles 80 C open squares 60 C open diamonds 40 C crosses 20 C filled circles and -10 C open triangles . From Cole et al. 2007. Copyright 2007 American Institute of Physics . Ban et al. 2003a Ban et al. 2003b . Very briefly this formalism considers a single-crystal compositionally graded ferroelectric bar. It basically integrates free energies of individual layers taking into consideration the energy due to the polarization spontaneous and induced electrostatic coupling between layers due to the polarization difference and the elastic interaction between layers that make up the graded heterostructure. The mechanical interaction arises from the electrostrictive coupling between the polarization and the selfstrain and consists of two components the biaxial elastic energy due to the variation of the self-strain along the thickness and the energy associated with the bending of the ferroelectric due to the inhomogeneous elastic deformation. Based on this approach the temperature 166 Ferroelectrics - Material Aspects dependence of average dielectric response of compositional BST with the same nominal composition BST75 25 can be calculated using average thermodynamic expansion coefficients and elastic constants available in the literature Mitsui et al. 1981 as shown in Fig. 10. In comparison with a sharp peak of the dielectric permittivity at Tc for bulk homogenous .
