Experimental manifestations of the Nb^{4+}-O^{-} polaronic excitons in KTa_{0.988}Nb_{0.012}O_{3}

R. V. Yusupov; I. N. Gracheva; A. A. Rodionov; P. P. Syrnikov; A. I. Gubaev; A. Dejneka; L. Jastrabik; V. A. Trepakov; M. Kh. Salakhov

doi:10.1103/physrevb.84.174118

arXiv · 1109.5253

Experimental manifestations of the Nb^{4+}-O^{-} polaronic excitons in KTa_{0.988}Nb_{0.012}O_{3}

R. V. Yusupov·I. N. Gracheva·A. A. Rodionov·P. P. Syrnikov·A. I. Gubaev·A. Dejneka·L. Jastrabik·V. A. Trepakov·M. Kh. Salakhov

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Abstract

The formation of the photo-polaronic excitons in ABO_{3} perovskite type oxides has been detected experimentally by means of the photoinduced electron paramagnetic resonance studies of KTa_{0.998}Nb_{0.012}O_{3} crystals. The corresponding microwave X-band spectrum at T < 10 K consists of a narrow, nearly isotropic signal located at g ~ 2 and a strongly anisotropic component. The first signal, which has a rich structure due to hyperfine interactions with the lattice nuclei, is attributed to the single trapped charge carriers: the electrons and/or the holes. The anisotropic spectrum is caused by the axial centers oriented along the C_{4} pseudo-cubic principal crystalline axes. The spectrum angular dependence can be described well by an axial center with S = 1, g_{\parallel) = 0.82, g_{\perp} = 0.52 and D = 0.44 cm^{-1}. The anisotropic spectrum is attributed to the Nb^{4+}-O^{-} polaronic excitons. The temperature dependence of the anisotropic component is characterized by two activation energies: the internal dynamics activation E_{a1} = 3.7\pm0.5 meV, which makes the EPR spectrum unobservable above 10 K, and the destruction energy E_{a2} = 52\pm4 meV. By comparing the anisotropic photo-EPR spectrum and the photoinduced optical absorption temperature dependencies, we found that the Nb^{4+}-O^{-} polaronic excitons also manifested themselves via the ~0.7 eV wide absorption band arising under UV light excitation in the weakly concentrated KTaO_{3}:Nb crystals.

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R. V. Yusupov, I. N. Gracheva, A. A. Rodionov, P. P. Syrnikov, A. I. Gubaev, A. Dejneka, L. Jastrabik, V. A. Trepakov, M. Kh. Salakhov. 2011-09-24. Experimental manifestations of the Nb^{4+}-O^{-} polaronic excitons in KTa_{0.988}Nb_{0.012}O_{3}. https://doi.org/10.1103/physrevb.84.174118

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