Single crystals of Bi2Sr2‐xCuO6‐y were grown from CuO‐rich melts. The Sr content in the crystals was varied from x=0.1 to x=0.5 by varying the starting composition of the melt and the oxygen content was adjusted using an appropriate heat treatment of the crystals in a thermogravimetric system. With decreasing Sr content the superconducting transition temperature,Tc, of the crystals decreased rapidly from 10 K to below 4.2 K and the resistivity in the a‐b plane changed from metallic (linear in T from 30 to 300 K) to semiconducting. Reducing the oxygen content in the crystals had a similar effect on the resistivity. Only crystals with close to the maximum oxygen content (y=0) were superconducting, and removal of oxygen from previously superconducting crystals resulted in a rapid decrease of Tc , and the eventual loss of superconductivity (Tc < 4.2 K). Although crystals of Bi2Sr2‐xCuO6‐y could be made sequentially superconducting‐semiconducting‐superconducting by the addition‐removal‐addition of oxygen, the process was not totally reversible. After only one such cyclic heat treatment x‐ray diffraction indicated that for some compositions such cycling resulted in the appearance of CuO and an another layered structure that has been identified previously and is slightly deficient in CuO. The new layered structure is semiconducting and has a layer‐stacking repeat distance that is 1 å smaller than the superconducting “221” phase.

The stable phase that forms near 2:2:1 in the Bi‐Sr‐Cu oxide system is now recognized as a semiconducting phase structurally distinct from the n = 1 Bi‐cuprate superconductor, whose actual composition (Bi2Sr2‐xCuO6‐y, x= 0.1‐0.25, y=0‐0.5) is deficient in Sr. The 2:2:1 phase forms by a slow solid‐state replacement of the superconducting phase for compositions near 2:2:1. It also can be grown from melt compositions involving several phase assemblages, but single‐phase products are not obtained, implying incongruent melting. Alumina and zirconia crucibles promote the growth of the superconducting phase by reacting with the melt to remove Sr, whereas Au crucibles promote the growth of the 2:2:1 phase. Owing to its fine‐grained, fibrous habit, structural characterization has been difficult. Of the unit cells proposed, the C‐centered monoclinic cell of Roth et al. provides the best fit to our x‐ray powder and single‐crystal precession data, a = 24.522(9), b = 5.426(2), c = 21.983(9) Å, β = 105.00(3)°. Perfect prismatic cleavages intersecting at ‐148° and ‐32° are indexed as {100} and {‐201} forms. Although, the superconducting n = 1 Bi‐cuprate exhibits variable Sr and O contents, the 2:2:1 phase appears to be a single composition with no oxygen exchange observed by TGA, although it may be somewhat deficient in Cu. The 2:2:1 phase is semiconducting as determined by electrical resistivity measurements, with an apparent activation energy of 0.013 eV. For a 2:2:1 stoichiometry, the measured density of ‐7.2. g/cm3 implies 16 formula units per cell.

The structure/property relationships in the Bi‐Sr‐Cu‐O system near Bi2Sr2CuOx have been investigated. The properties and phase limits of the solid solution Bi2+xSr2_yCuO6±δ have been determined and a structural model for Bi2Sr2CuO6 is proposed.

Novel superconducting thallium cuprates of the type T1Ca1‐X LnX Sr2 Cu2O6+δ (Ln = Y or rare earth), T1Srn+1‐x Lnx Cun OY and Tl1‐x PbX Srn+1Cun08+δ are described. These cuprates as well as Bi2Ca1‐x Lnx Sr2Cu2O8+δ and TICa1‐xYxBa2 Cu2 O6+δ . show maximum T around a specific composition or oxygen content. They also show interesting changes in the sign and magnitude of the thermopower with the composition. Specially noteworthy is the negative slope of the thermopower‐temperature plots. The thermopower behaviour in these two‐band systems can be understood in terms of entropie and quasiparticle contributions. It appears that Tl1‐x Pbx CaSr2Cu2O6+δ is a genuine high T electron superconductor.

Superconductive 2:2:1:2 phases of the type Bi2Sr2Ca1-yLnyCu2O8+x+y/2, where Ln stands for Yb or Er, have been synthesized and characterised by X-ray and electron diffraction. The small rare earth atoms prove to substitute preferentially in the Ca site. The electrical properties as well as the structural characteristics of these compounds are affected by the rare earth substitution rate. It is shown, in particular, that the long axis parameter of the subcell and the incommensurate period of the modulation decrease with increasing y. The substitution of trivalent cations for Ca requires the presence of additional oxygen atoms in the structure, the location of which is discussed.

Phase assemblages in two Sr-Bi-Pb-Ca-Cu-O glasses and their crystallization into glass-ceramics through a sequence of heat treatments are described. Samples were heat treated at various temperatures based on differential thermal analysis (DTA) analysis of the as-quenched glasses. X-ray powder diffraction was used to identify the compounds in each sample; and the different phases formed in these two samples were compared. Results of microstructural characterization of selected samples using scanning electron microscopy are discussed.

High temperature neutron powder diffraction has been used to study the formation of the 110K transition temperature material, Bi2Ca2Sr2Cu3Ox (2223), both from synthetic reaction mixtures and after partial melting. The results indicate that the 80K transition temperature material, Bi2CaSr2Cu2Ox (2122), is the precursor to the (2223) material. The reaction to form the (2122) occurs rapidly at 860°C, while the conversion of this material to the (2223) is much slower.

A high resolution neutron powder diffraction experiment has been performed on Bi4Sr8Cu5O19+x. The structure is well described in the space group Fmmm with the oxygen atoms in the bismuth planes appearing disordered in intermediate positions between NaCl and bridging sites as occurs in the superconductors Bi2Sr2Can‐1CunO4n+2. Temperature dependence study of powder neutron diffraction patterns between 1.5K and 998K does not show any relevant structural change neither evidence of antiferromagnetic ordering in this sample.

Results are presented for 850°C oxygen annealing experiments (up to 62 hr) on the 2122 (Tl:Ca:Ba:Cu) oxide phase, with and without intermediate grinding. Samples were characterized by powder X-ray diffraction and a.c. magnetic susceptibility. The 2122 phase appears to be thermodynamically stable in oxygen under conditions of both extensive grinding, and, annealing of long duration. However, onset Tc's vary from 71 K to 109 K for apparently single-phase 2122 samples with nearly identical X-ray powder patterns, depending upon the heat treatment.

We have examined several crystals belonging to the Tl‐2122 structure type (Tl2CaBa2Cu2O8 with c=29Å), and have shown that cation solid solution occurs. Such cation disorder appears to be responsible for the observed small differences in lattice parameters reported by various investigators and to contribute towards the substantial variation in the superconducting transition temperatures.

We have determined the crystal structures of five phases in the Bal-xKxBiO3 system for 0≤x≤0.5 and 10K≤T≤473K. Superconductivity occurs only in a cubic perovskite phase with the maximum Tc at the transition to an orthorhombic, Ibmm, phase. The commensurate structure of this orthorhombic phase, which involves only tilting of the Bi06 octahedra, provides no explanation for its non-metallic behavior. However, an incommensurate structural modulation, observed by electron diffraction, may provide a rationalization. Thus, the maximum Tc at the phase boundary may result from competition between superconductivity and a charge density wave. Further studies of the phase diagram at high temperatures, where controlled oxygen atmospheres are required, reveal an unusual reentrant formation of a potassium-containing impurity phase which explains the need for synthesis techniques that involve initially reacting in a reducing atmosphere, followed by oxygenation at lower temperature.

Single‐phase samples of (Ba1‐xKx)(Bi1‐xSby)O3 have been synthesized over a limited compositional range using a two‐step procedure: high‐temperature firing in a low oxygen partial pressure followed by low‐temperature oxygen annealing. For y=0 and 0.37<x<0.50, samples have a simple cubic structure and are bulk superconductors with Tc gradually decreasing from 30 to 22K as x increases to 0.50. For fixed x and y>0 samples are superconducting again with a simple cubic structure and with Tc gradually decreasing as y increases.

Samarium‐based oxyfluoride analogs of the apparently “n‐type” 24 K superconductor, Nd1.85Ce0.15CuO4, were prepared. A series of compounds with general formula Sm2‐xCexCuO4‐yFy were prepared and characterized by X‐ray diffraction, bromo/iodometric titration, and measurements of electrical resistivity. Homogeneous superconducting phases have not yet been obtained; preliminary results and discussion of property trends are presented.

We have controlled the carrier (electron) density in Nd2CuO2 of the T’ structure by introducing both Ce and Ca into the Nd‐sites, and studied the superconducting transition temperature versus carrier density relationship. The phase relations in the (Nd1‐x‐yCexCay)2CuO4‐z system were studied by means of powder X‐ray dirfractron and electron‐probe micro‐analysis techniques. For the phase diagram of the (Nd1‐x‐yCexCay)2CuO4‐z system, the single phase field of the T’ phase was established. Samples of the (Nd0.9‐yCe0.1Cay)2CuO4‐z system with compositions included in the single phase field were synthesized. The carrier density in these samples was varied by controlling the Ca content. The Hall effect and DC resistivity were measured to elucidate the relation between Tc and the carrier density.

Eu2.xCexCuO4±δ (0 ≤ x ≤ 0.17) has been synthesized with the tetragonal T’ structure. AC susceptibility and resistance measurements show that Eu2‐xCexCuO4±δ becomes superconducting with τc∼13 K for x= 0.15 and 0.17, when prepared under reducing conditions. The 151Eu Mossbauer shift shows that the Euvalence falls into a narrow range near Eu 3+ . The temperature dependence of the Mossbauer absorption yields a Debye temperature of 319 K for the Eu ion in Eu1.85Ce0.15CuO4±δ

We have investigated single‐crystals growth of Nd2‐xCexCu04‐y By using a flux method. The phase diagram Nd203 ‐CuO has been determined For a number of compositions. In addition, the corresponding diagram for some Nd2O3CeO2‐CuO composition is also reported. Plate single crystals having dimensions up to 5 x 5 x 0.2 m have been prepared by the melt mixtures from 1250℃ to 800℃ at a rate of 5℃/h.

The yield of CeO2 concentration in the starting compositions and the corresponding x values in the crystals has been investigated in order to improve superconducting properties of the crystals. Superconducting single crystals have been found from flux compositions 70% CuO, (30‐z)% NdO1.5and z% of CeO2 with 2.50 < z < 4 5.

The n‐type superconductor, Nd1.85Ce0.15CuO4‐δ has been prepared by solid state reaction and solution precursor techniques under various conditions and characterized by means of X‐ray diffraction, magnetic susceptibility, electrical resistivity and SEM measurements. Samples prepared by solution method displayed higher normal state resistance but better superconducting volume fractions than those prepared by conventional ceramic techniques. In addition, the solution precursor technique reduces the sintering temperature from 1150°C (used for solid‐state route) to 1000°C in achieving the superconducting phase. The solution‐route yields particles with relatively uniform size distribution, but poor connectivity between the grains. In contrast, the solid state preparations yield well connected grains but with a larger distribution of sizes. The observed differences in the superconducting properties of samples prepared by different techniques have been attributed to the differences in their microstructure.