The long-time correlations induced by defects in the quantum paraelectrics and

Abstract

The long-time correlations of fluctuations of lattice displacements in the quantum paraelectrics and are studied within the framework of the mode-coupling theory of the dynamic transition from an ergodic to a non-ergodic state caused by defects. It is shown that the very hard local non-symmetry-breaking defects formed by the oxygen vacancies can induce the dynamic transition at . The low-temperature non-ergodic state is characterized by long-time correlations of local fluctuations of the polar displacements, which continuously arise for . Simultaneously, the local non-symmetry-breaking defects lead to the appearance of long-time correlations of long-wavelength fluctuations of acoustic displacements via the local random piezoelectric coupling for . The random local piezoelectric coupling is caused by the electrostrictive interaction, which is modified by the random electric fields of the frozen symmetry-breaking defects. The conditions that must be met for the dynamic transition to be induced by the oxygen vacancies are analysed. It is also shown that the unavoidable oxygen vacancies in the nominally pure and are quite sufficient in number to cause the non-ergodic state. The role of the dynamic transition in the formation of the glass state for lightly doped and is discussed.

Induced polarized state in intentionally grown oxygen deficient KTaO3 thin films

“…It is important to note that the film thickness is about 230 nm, and at this point, the films should be elastically relaxed. However, oxygen vacancies, intentionally incorporated during the deposition procedure, induce lattice distortions on the TaO 6 octahedron 21 and expansion of the unit cell, 30,31 which together with extrinsic stresses associated with lattice mismatch and thermal mismatch between the substrate and thin film material and intrinsic stresses associated with impurities or defects like grain boundaries or dislocations lead to such a deviation between oxygen deficient KTaO 3 thin films and single crystals. The thermal mismatch plays an import role in this situation due to the large difference between the coefficient of thermal expansion of the KTO and the platinum.…”

“…For example, a very interesting type of defect 18 and at the same time capable to induce a polar state in the KTaO 3 system is the introduction of oxygen vacancies which can lead to lattice distortions as reported in other perovskites. [19][20][21] Oxygen deficiency can be intentionally achieved in different ways, like nonstoichiometric growth, extrinsic doping, or in nonannealed samples. 22 Moreover, in cubic perovskites, the symmetry of electronic states localized near the oxygen vacancy may be spontaneously broken if the electron-lattice interaction overcomes kinetic energy of electron motion.…”

Energetic, Electronic, and Optical Properties of Intrinsic Charge Carrier-Trapping Defects in KTaO3: Insights from a Hybrid DFT Study

“…Usually, the observed properties of such materials are strongly governed by the presence of intrinsic defect and chemical compositions of the material. Defect physics is considered to be one of the most challenging issues that need to be explored. − The presence of defects can modify the macroscopic properties of a material either negatively or positively. Interestingly, oxygen vacancies are found to play an important role in the ferroelectric properties in KTaO 3 . − Besides, for multipurpose applications, these materials may have to face different extreme conditions and high radiation environments, which can result in the formation of different defects in the host matrix.…”

Normal and abnormal dielectric relaxation behavior in KTaO3 ceramics

“…Due to this, a plethora of experimental and theoretical investigations have been performed on the low-temperature dielectric properties of KT. [1][2][3][4][5][6][7][8][9][10] Among perovskite materials, the appealing dielectric properties of low dielectric loss and relatively high dielectric permittivity for KT make it attractive for study as a promising microwave material. [11][12][13][14] On the other hand, KT crystal has highly polarizable lattice, which allows strong interaction of impurity-induced dipoles leading to dipole glass state 15 and even to ferroelectric phase transition.…”