The properties of the Y1−xPrxBa2Cu3O7 (YPrBCO) system are reviewed. These include superconducting, normal state, structural, chemical, optical, magnetic, and thermal properties. The destruction of superconductivity with Pr doping is discussed in view of possible models such as hole filling, localization, magnetic pair-breaking, and the role of hybridization. Applications to electronic devices using YBCO/PrBCO/YBCO multilayers are also reviewed.

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A review of the superconducting and normal state properties of Y1−xPrxBa2Cu3O7

The crystal structure, superconductivity and magnetic properties of the title compounds have been investigated. The results revealed that with the concentration of Pr being constant, the transition temperatureTc of this system decreases with the increasing of La, or rather with the increasing of effective ionic radii of rare earth elements and the superconductivity disappears at aboutx=0.6. The coefficient of electron specific heat and the density statesN (0) which were infered from the magnetic measurements also decrease with the increasing of the effective radii. The relation between the radii of rare earth elements and hybridization is briefly discussed.

Superconductivity and magnetic properties in Pr0.2Yb0.8−xLaxBa2Cu3O7−δ

The crystallographic changes that occur with increasing Pr concentration in the Y−xPrxBa2Cu3O7−δ system have been studied by neutron diffraction. As x is increased from 0 to 1, the orthorhombic a, b and c lattice parameters expand monotonically, while the orthorhombic distortion, espressed as b a , decreases, reflecting increased occupation of O(5) sites at the expense of O(4) chain site occupancy. The separation of the CuO2 planes in PrBa2Cu3O7−δ indicates that the Pr ions have an intermediate valence of ∼3.3 in this compound. Evidence is presented for increased interaction between the Pr ions and oxygen ions in adjacent CuO2 planes.

Neutron diffraction study of Pr valence and oxygen ordering in the Y1−xPrxBa2Cu3O7−δ system

Publisher Summary This chapter discusses the structural studies performed on superconducting oxides. It focuses primarily on Y 1 Ba 2 Cu 3 O 7–δ , nicknamed the 123 structure, because this structure has been the most extensively studied to date. The chapter describes the basic atomic arrangements in Y 1 Ba 2 Cu 3 O 7–δ and the way these arrangements change as a function of processing. The defects that are commonly found in the 123 structure are discussed, some of which play a dominant role in controlling superconducting properties. The studies of elemental substitutions for Y, Ba, Cu and/or O in 123 are summarized, and 123 with the other families of superconducting oxides is compared. These studies have both theoretical and practical interest because they provide clues to the roles that various structural features play in the mechanism of high-temperature superconductivity, which, in turn, may aid in the discovery of even higher temperature superconductors. It is evident from the variety of behaviors exhibited by 123 after different processing conditions that the structure has considerable flexibility. The oxygen stoichiometry can be varied over a wide range, and different cations can be substituted at least partially into every site.

The Structure of Y1Ba2Cu3O7-δ and its Derivatives

The 90 K superconductor, YBa 2 Cu 3 O δ (YBCO), has proved to be highly adaptable chemically as it can accommodate a wide variety of cationic and anionic substitutions. Indeed, the majority of the chemical elements, excluding noble gases and actinides, have been reported to substitute to some extent into the YBCO structure. This review covers the literature on such substitutions and their effect on the properties of YBCO. Reported solubility limits are given, together with crystal symmetry and trends in unit cell parameters with dopant concentration. The dopant site is considered; this is additionally complex in the case of copper substitution because of the two distinct copper sites in the crystal structure. The effect of the dopant on the critical temperature, T c , is reviewed; the literature is often contradictory due to the dual effects of variable oxygen content and the nature of the dopant. Preparation methods appear to have an effect on solubility limits, crystal symmetry and T c , Also, the methods used to determine solubility limits are often imprecise which can lead to contradictions. The magnetic properties of doped materials are reviewed; for some dopants, particularly the magnetic lanthanides, antiferromagnetism and superconductivity co-exist. The related RBa 2 Cu 3 O δ phases (R = lanthanide), their structure, properties and behaviour on doping are reviewed in a similar way. For the larger rare earths, the related systems R 1+ x Ba 2- x CU 3 O δ , are reviewed; as x increases, the transition temperature decreases and compositions R 1.5 Ba 1.5 Cu 3 O δ are semiconducting. The upper and lower solubility limit changes with R, and for R = Dy, the upper limit is x = 0 composition, LaBa 2 Cu 3 O δ , cannot be prepared in air since substitution of La onto the Ba site occurs, forming the Ba-deficient solid solutions. The discovery of superconductivity above liquid nitrogen temperatures in YBa 2 Cu 3 O 7 , has generated a vast quantity of research; to date, > 20 000 papers have appeared on the 123 materials (source: BIDS). This review, therefore, cannot be comprehensive, but attempts to highlight important substitutions, their effect on the properties of YBCO and any contradictions in the literature.

Crystal chemical substitutions and doping of YBa2CU3Ox and related superconductors

A series of Ba2(Y1−x
Pr
 x
 )Cu3O9−y
 solid solutions were prepared with the orthorhombic distorted perovskite structure. The compound Ba2PrCu3O9−y
 belonging to tetragonal system is a good semiconductor. The superconductivity is observed for samples withx<0.6. With the increase of Y content, the distortion of crystal structure is greater and the superconductive transition temperature of zero resistanceTc(0) raises.

G. H. Rao

Papers

The superconductive properties and crystal-structure of ba2(y1-xprx)cu3o9-y solid-solutions