Pressure-induced crossover from long-to-short-range order in [Pb(Zn 1/3 Nb 2/3 )O 3 ] 0.905 (PbTiO 3 ) 0.095 single crystal Using the first-principle calculations, we investigate in detail the structure instability resulting from softening of the polar zone-center phonon mode ͓ferroelectric ͑FE͒ instability͔ and nonpolar zone-boundary mode ͓antiferrodistortive ͑AFD͒ instability͔ in cubic BaZrO 3 ͑BZO͒ under hydrostatic pressure P from Ϫ20 to 90 GPa. The hydrostatic pressure enhances the AFD instability, while it suppresses and then enhances the FE instability. A sequence of FE→ cubic→ AFD → AFD/ FE phase transitions with increasing P is predicted. A careful examination of the pressure dependence of full phonon dispersions and interatomic force constants in real space reveals the microscopic key interactions in driving the transitions. With increasing pressure P, the drastically evolving short-range forces suppress the FE instability induced by the long-range dipole-dipole forces under low pressure, and enhance both the AFD and FE instability under high pressure. We investigate the dielectric properties of cubic BZO under hydrostatic pressure. The dielectric constant as a function of pressure shows a minimum contributed from the TO 1 mode with the lowest frequency. We argue that this pressure dependence of the dielectric constant mainly originates from fluctuations of the SR forces.
(A and B) CV curves of (A) Li2ZnTi3O8/C and (B) Li1.9K0.1ZnTi3O8/C, (C) Initial charge–discharge curves and (D) cycling capacity and (E) rate performances of Li2ZnTi3O8/C and Li1.9K0.1ZnTi3O8/C. (F) The composition of the CR2032 cell.
The traditional BaTiO3/PbTiO3 ferroelectric material has excellent performance and is widely used, but the Pb in the material has polluted the environment. Studies have found that other ferroelectric materials can also have good performance after doping and improvement. The problem is that the development is too slow. If a reasonable explanation can be given for the changes from the original structure, the research and development process will be accelerated. In this paper, we investigated the ferroelectric properties at the orthogonal-crystal KNbO3 using first-principles calculations coupled with a phenomenological theory model. By replacing the K atoms with Na, studying the stability, polarization, energy band, and density of states after replacement doping, explaining the internal mechanism of its generation, and providing theoretical support for the research and development of new materials.
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