Physical characterization of pure and substituted tetragonal LaBaCaCu3O7-delta superconductor

The high T-c superconductor, forming the focus of the present review, prese nts an interesting situation where, despite its oxygen content close to 7.0 , the system prefers to crystallize in tetragonal structure, as distinct fr om exhaustively studied orthorhombic RE:123 (REBa2CU3O7, RE = rare earth) c ompounds. Its optimum T-c is decided by the cation intermixing at various s ites, unlike that in case of normal RE:123, where all cationic sites are fu lly occupied and fixed, leaving the anionic sites free for oxygen filling. In this, we review the rich crystal chemistry of this compound and discuss it in conjunction with its unusual superconducting properties. The article is divided in five parts: (1) first we discuss variously reported interesti ng finer structural details and superconductivity of pristine LaBaCaCu3O7-d elta (La:1113) superconductor. The La, Ba and Ca sites are found to be inte rmixed with respect to their nominal sites of the standard RE:123 structure . (2) We examine the structural aspects and superconductivity of La1-xRExBa CaCu3O7 RE = Nd, Dy, Sm and Pr). Unlike RE:123 and 124 compounds, the RE: 1 113 compounds form only with light rare earths such as La, Pr and Nd. Pr:11 13 compound is found to be an insulator with Pr moments ordering magnetical ly at around 8 K, unlike at 17 K for Pr:123. (3) Studies of Pr substitution reveal that relative T-c depression due to Pr in the (La,Nd)(1-x)PrxBaCaCu 3O7 system is less in comparison to that found for La or Nd site Pr substit uted (La,Nd)(1-x)PrxBa2Cu3O7. (4) The results of superconductivity and stru ctural details are reviewed for LaBaCaCu3-xMxO7 (M = Fe, Co, Ni, Ga and Zn) and finally (5) we summarize our conclusions. The results in terms of T, d epression due to these impurities in the parent La: 1113 system are seen as similar to those observed for RE:124 (REBa2CU4O8) and Nd:214 (Nd2-xCexCUO4 ), but are different from RE:123 and La:214. The results of structural deta ils, superconductivity and magnetic ordering presented in the four parts fo r La1-xRExBaCaCu3-yMyO7 (RE = Nd, Dy, Sm, Pr with 1.0 greater than or equal to x greater than or equal to 0.0, and M = Fe, Co, Ni, Ga and Zn with 0.24 greater than or equal to y greater than or equal to 0.0 were obtained from X-ray and neutron diffraction and using AC and DC magnetic susceptibility, electrical resitivity and heat capacity data as a function of temperature. This review is mainly a consolidated work of the authors, including their collaboration from various laboratories and the reported data of other work ers, all being duly acknowledged in the text.