Part of the phase diagram of the La 2 O 3- CuO system has been studied and single crystals of La 2 CuO 4, (LaSr) 2 CuO 4 (up to 20 × 8 × 6 mm 3), YBa 2 Cu 3 O 7−δ (up to 8 × 6 × 0.1 mm 3) and HoBa 2 Cu 3 O 7-(up to 3 × 2.5 × 1 mm 3) have been grown by the method of spontaneous crystallisation, using a rotational crucible. It has been established that thermal treatment of "123" single crystals under oxygen pressure to 10 bars improves their superconducting properties. Electrical, magnetic, optical properties, and the real structure of the single crystals produced have been studied.
AbstractThe optical properties of low-dimensional dielectric cuprates, including parent systems for high-temperature superconductors, such as La_2CuO_4, Sr_2CuO_2Cl_2, and YBa_2Cu_3O_6 are briefly reviewed. The main focus is on the d – d and p – d charge transfer transitions, which determine the fundamental absorption band. The analysis of optical properties shows the instability of parent cuprates against the d – d charge transfer with the formation of metastable electron–hole (EH) dimers of the Cu^1+–Cu^3+-type pairs coupled by the two-particle transfer and characterized by the giant electric polarizability. The formation of a system of stable EH dimers upon nonisovalent substitution determines the unconventional properties of the pseudogap and superconducting phases of doped cuprates.
Оптическая спектроскопия и сверхпроводимость купратов (О б з о р)
