HIGH-TEMPERATURE SUPERCONDUCTORS

Poly and single-domain crystals of TmBa₂Cu₃O_7-d

Works on the synthesis and study of the high-temperature superconductors of various structural types has begun in our Laboratory shortly after their discovery. The first results has been published at the International Conference on HTSC, Interlaken, 1988.

Since all these materials have incongruent character of melting, the flux growth has to be used. This method allowed to grow cm-sizes high-quality single crystals of the La_2-xM_xCuO₄ (M = Ca, Sr, Ba), Ln_2-xCe_xCuO₄ (Ln = Pr, Nd, Sm, Eu, Gd), RBa₂Cu₃O_7-d (R = Y, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb), Bi₂Sr_{2- x}Ca_xCuO_6+y, Bi₂Sr_3-xCa_xCu₂O_8+y.

The main attention was paid to RBa₂Cu₃O_7-d crystals. Influence of the kind of rare-earth elements, isomorphous substitutions, crystal growth conditions such as the melts composition, cooling rate, surrounding atmosphere, was studied. The best superconducting properties with the T_C = 89-93 K and the transition width of about 0.2 K were found for the crystals with Tm and Y. Some of these crystals were free from twins and suitable for precision investigations of the atomic structure and physical properties. Furthermore, a new effective method of detwinning was worked out which consists of thermomechanical treatment of crystals under reduced oxygen partial pressure. It was found that the crystals with a few large domain can show sharp anomalies of conductivity at the superconducting transitions which may be attributed to a small difference of T_C value (~ 1K) in the vicinity of the twin boundaries and in the bulk of crystals. The single domain crystals were used for the studies of their atomic structure, lattice dynamics, vortex pinning and other properties.

Main publications:

1. Crystal growth and properties of the RBa₂Cu₃O_7-y - family crystals. V.I.Voronkova, I.V.Vodolazskaya, V.K.Yanovskii. Superconductivity: Physics, Chemistry, Technique, 1989, v.2, p.50.

2. Behavior of the superconducting compounds RBa₂Cu₃O_7-y at high temperatures. V.K.Yanovskii, V.I.Voronkova, I.V.Vodolazskaya, I.N.Leont'eva, T.P.Petrovskaya. Superconductivity: Physics, Chemistry, Technique, 1989, v.2, p.40.

3. Single crystals of La_2-xSr_xCuO_4-y. V.I.Voronkova and V.K.Yanovskii. Superconductivity: Physics, Chemistry, Technique, 1989, v.2, p.81.

4. Single-domain crystals of YBa₂Cu₃O_7-d and TmBa₂Cu₃O_7-d. V.I.Voronkova, I.V.Vodolazskaya, and V.K.Yanovskii. Physica C, 1989, v.162-164, p.1211.

5. Growth and superconductivity of the Bi₂Sr_2-xCa_xCuO_6+d and Bi₂Sr_3-xCa_xCu₂O_8+d single crystals. V.I.Voronkova, A.A.Gippius, V.V.Moshchalkov, V.K.Yanovskii. Superconductivity: Physics, Chemistry, Technique, 1990, v.3, p.1135.

6. Synthesis of single domain superconductor TmBa₂Cu₃O_7-d and its atomic structure. V.I.Voronkova, V.K.Yanovskii, V.N.Molchanov, N.I.Sorokina, V.I.Simonov. JETP Letters, 1990, v.52, p.224.

7. Bi-based superconductors and their surface wave velocities. V.V.Aleksandrov, T.S.Velichkina, V.I.Voronkova, A.A.Gippius, S.V.Red'ko, I.A.Yakovlev, and V.K.Yanovskii. Solid State Commun., 1990, v.76, p.685.

8. The full Meissner effect in the untwinned TmBa₂Cu₃O_x single crystal. V.V.Moshchalkov, A.A.Zhukov, V.D.Kuznetsov, V.V.Metlushko, V.I.Voronkova, V.K.Yanovskii. Solid State Commun., 1990, v.74, p.1295.

9. Hypersound studies of the electron doped Ln_2-xCe_xCuO₄ and hole doped La_2-xM_xCuO₄ high-T_C single crystals. V.V.Aleksandrov, T.S.Velichkina, I.V.Vodolazskaya, V.I.Voronkova, I.A.Yakovlev, and V.K.Yanovskii. Solid State Commun., 1992, v.82, p.669.

10. Thermomechanical detwinning of superconducting YBa₂Cu₃O_7-x single crystals under reduced oxygen partial pressure. V.I.Voronkova, V.K.Yanovskii, and Th.Wolf. Superconductivity: Physics, Chemistry, Technique, 1993, v.6, p.1529.

11. Growth, morphology and superconducting properties of TmBa₂Cu₃O_7-d single crystals. V.I.Voronkova, V.K.Yanovskii, Th.Wolf, E.W.Seibt, A.A.Zhukov, S.A.Klestov, V.N.Molchanov, N.I.Sorokina, V.I.Simonov. J.Crystal Growth, 1995, v.149, p.74.

12. Growth, detwinning and properties of YBa₂Cu₃O_x and TmBa₂Cu₃O_x single crystals. V.I.Voronkova, V.K.Yanovskii. Growth of Crystals. V.20. Consultants Bureau, N.Y.,1996, pp.153-169.

13. Ferroelastic domains in RBa₂Cu₃O_7-d crystals. V.I.Voronkova and V.K.Yanovskii. Ferroelectrics, 1997, v.191, p.275.

14. Single domain superconductor TmBa₂Cu₃O_7-d: Crystal growth and atomic structure. N.I.Sorokina, V.N.Molchanov, V.I.Voronkova, V.K.Yanovskii, V.I.Simonov. Crystallography Reports, 1999, v.42, p.567.