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Pseudorotational Averaging of EPR Spectrum of Cu(II)O_{5} Complex in YBa_{2}Cu_{3}O_{7-δ} in Low Temperatures

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Stankowski J., Kempiński W., Trybuła Z.

Acta Physica Polonica A

1991

vol. 80

issue 4

571-581

In low temperatures the condensation of oxygen was found to occur at 05 site in an elementary cell of YBa_{2}Cu_{3}O_{7-δ} being the fifth ligand forming the CuO_{5} complex around Cul copper in chain. This change of coordinantion from CuO_{4} to CuO_{5} is the origin of a pseudorotation related to a strong vibronic coupling of two distorted configurations: a tetragonal pyramid C_{4v} and a trigonal bipyramid D_{3h}, which yields a pseudocubic EPR spectrum in low temperatures. The averaged spectroscopic splitting coefficient is related to a superposition of vibronically coupled orbital states |x^{2} - y^{2}〉 and |3z^{2} - r^{2}〉. The averaged spectrum was for the first time observed in low temperatures since the oxygen condensation in YBa_{2}Cu_{3}O_{7-δ} at 05 site of the chain occur only when oxygen undergoing fast diffusion among the chains, gets localized with decreasing temperature. The activation energy of oxygen desorption from the 05 site is 36 K.

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1 Acta Physica Polonica A

1 1991

1 Kempiński W.

1 Stankowski J.

1 Trybuła Z.

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Pseudorotational Averaging of EPR Spectrum of Cu(II)O_{5} Complex in YBa_{2}Cu_{3}O_{7-δ} in Low Temperatures