Fakultät für Physik und Geowissenschaften, Universität Leipzig, Linnéstraße 5, D-04103 Leipzig, Germany.
J Phys Condens Matter. 2010 Feb 17;22(6):065902. doi: 10.1088/0953-8984/22/6/065902. Epub 2010 Jan 27.
Electron paramagnetic resonance (EPR) spectra of Cr5+ defects incorporated on Ti(4+) sites in powdered ceramics of PbTiO3 were investigated in the temperature range 50-400 K at 9 GHz (X), 34 GHz (Q) and 94 GHz (W band). The [Formula: see text] Jahn-Teller effect stabilizes the vibronic ground state of the 3d(1) electron of the Cr(5+) ion and leads to a tetragonally distorted defect- O6 octahedron with the point symmetry D(4h). The spontaneous electrical polarization present in the ferroelectric phase of PbTiO3 appears as a further perturbation producing an additional g-tensor contribution by the quadratic field effect. Its symmetry is dependent on the orientation of the electrical polarization with respect to the Jahn-Teller distortion axis, the tetragonal axis of the defect- O6 octahedron. If the polarization of a domain is anti- or parallel to this axis, the local tetragonal symmetry of the Cr5+ ion persists whereas it is reduced by a perpendicular orientation. Anisotropic EPR spectra of tetragonally and orthorhombic distorted Cr(5+)O6(12-) are detected at low temperatures. Increasing the temperature, the peaks of the two spectra are broadened and a motionally averaged isotropic spectrum appears at 200 K.
在 9 GHz (X)、34 GHz (Q) 和 94 GHz (W 波段) 下，研究了掺钛(4+)位 Cr5+缺陷的 PbTiO3 粉末陶瓷的电子顺磁共振(EPR)谱，温度范围为 50-400 K。[Formula: see text] Jahn-Teller 效应稳定了 Cr(5+)离子的 3d(1)电子的振动态基态，并导致具有点群 D(4h)的四面体畸变缺陷-O6 八面体。在 PbTiO3 的铁电相存在的自发极化表现为进一步的微扰，通过二次场效应产生附加的 g 张量贡献。其对称性取决于极化相对于 Jahn-Teller 畸变轴、缺陷-O6 八面体的四方轴的取向。如果一个畴的极化是反平行或平行于这个轴，Cr5+离子的局部四方对称性保持不变，而垂直取向会降低它。在低温下检测到了各向异性的四面体和正交畸变的 Cr(5+)O6(12-)的 EPR 谱。随着温度的升高，两个谱的峰变宽，在 200 K 时出现运动平均的各向同性谱。
