| Автор | R Valiente |
| Автор | M C Marco de Lucas |
| Автор | F Rodriquez |
| Дата выпуска | 1995-05-15 |
| dc.description | The charge-transfer electronic structure of CuBr<sub>4</sub><sup>2-</sup> in (N(CH<sub>3</sub>)<sub>4</sub>)<sub>2</sub>CdBr<sub>4</sub> crystals is investigated through polarized optical absorption spectroscopy. The transition energy and the band polarization are explained in terms of the Jahn-Teller distortions of D<sub>2d</sub> symmetry of the CuBr<sub>4</sub><sup>2-</sup> complex. Some bands are split in the low-temperature spectra by the spin-orbit interaction of the Br ligands. The results are compared with those available for other CuBr<sub>4</sub><sup>2-</sup> systems. We also investigate the dynamics of the inorganic CuBr<sub>4</sub><sup>2-</sup> units in the 9.5-300 K temperature range through the intensity of the charge-transfer bands. Analogously to the CdBr<sub>4</sub><sup>2-</sup> tetrahedra in the pure crystal, CuBr<sub>4</sub><sup>2-</sup> experiences reorientational motions upon varying the temperature which are correlated with the temperature dependence of the monoclinic beta parameter below the Pmcn to P2<sub>1</sub>c/ phase transition temperature T<sub>cl</sub>=272 K. An important finding of the present work is the observation of anomalies in the CuBr<sub>4</sub><sup>2-</sup> dynamics which are associated with the existence of a new first-order phase transition at T<sub>c2</sub>=20 K with a thermal hysteresis Delta T=10 K. This new phase transition, which had not previously been detected in the ((CH<sub>3</sub>)<sub>4</sub>N)<sub>2</sub>MBr<sub>4</sub> (M=Zn, Mn, Co or Cd) series, would correspond to the monoclinic P2<sub>1</sub>c/ to orthorhombic P2<sub>1</sub>2<sub>1</sub>2<sub>1</sub> transition, confirming the predictions of the universal p-T phase diagrams of the title compounds. |
| Формат | application.pdf |
| Издатель | Institute of Physics Publishing |
| Название | Charge-transfer spectra and dynamics of CuBr<sub>4</sub><sup>2-</sup> in (N(CH<sub>3</sub>)<sub>4</sub>)<sub>2</sub>CdBr<sub>4</sub>:Cu<sup>2+</sup> crystals: a new first-order phase transition at T<sub>c2</sub>=20 K |
| Тип | paper |
| DOI | 10.1088/0953-8984/7/20/008 |
| Electronic ISSN | 1361-648X |
| Print ISSN | 0953-8984 |
| Журнал | Journal of Physics: Condensed Matter |
| Том | 7 |
| Первая страница | 3881 |
| Последняя страница | 3894 |
| Аффилиация | R Valiente; Fac. de Ciencias, Cantabria Univ., Santander, Spain |
| Аффилиация | M C Marco de Lucas; Fac. de Ciencias, Cantabria Univ., Santander, Spain |
| Аффилиация | F Rodriquez; Fac. de Ciencias, Cantabria Univ., Santander, Spain |
| Выпуск | 20 |
