We have synthesized single crystals of Hg1−xAuxBa2Ca2Cu3O8+δ (Hg(Au)-1223) with nominal Au content in the range 0≤x≤0.20. The composition and the homogeneity of the crystals were studied by electron microprobe analyses and the lattice constants were determined by X-ray diffraction. The nominal composition of gold of x=0.05 corresponds to an optimum for growing stoichiometric Hg-1223 single crystals. Each individual crystal shows a homogeneous gold content but the amount of substitution varies from 0.08 to 0.14 from crystal to crystal. These crystals exhibit superconductivity at Tc=133 K.

Using a sensitive sc technique, we have measured the specific heat (C) of a small single crystal of HgBa2Ca2Cu3O8+delta in fields up to 7 T. In zero field the superconducting anomaly has the form of a quasilogarithmic peak, which is almost symmetric about T-c. In increasing fields the anomaly is strongly suppressed and is shifted to lower temperatures (with a slope of similar to -0.8 K/T). This unusual behavior is qualitatively different from that of YBa2Cu3O6.95, and seems to be intrinsic to the quasi-two-dimensional, high-T-c superconductors. We find that the three-dimensional XY model of critical fluctuations best describes our data.

The thermodynamic properties of Hg1201 have been studied by thermogravimetry in terms of point defects, related to the departure from stoichiometry delta. The oxygen intercalation/disintercalation process is shown to be not completely reversible in the temperature range of 150-450 degrees C. The reversible fraction delta* depends on the oxygen pressure according to a law in (pO(2))(1/6) which corresponds to the insertion of interstitial oxygen and the formation of two holes per oxygen. The formation enthalpy of these defects, 0.5 eV, is rather small. A model based on temperature dependent barrier heights is introduced to account for the non-reversible fraction. The barrier mechanism may be related to exchange interactions between interstitial oxygens mediated by the mercury sublattice. The thermogravimetric analysis has allowed to derive the T-c versus delta curve without resorting in particular in the overdoped regime to high oxygen pressures.

Single crystals and pure single phase powder material of HgBa2CuO4+δ (Hg-1201) have been obtained with the same single step synthesis technique under normal pressure conditions used to grow single crystals of HgBa2Ca2Cu3O8+δ (Hg-1223) [1]. X-rays structural investigations carried out on single crystals show no substitutional defects at the mercury site, in particular no mixed occupancy of copper, in contrast to the case of Hg-1223. Excess oxygen content appears to be present only in the basal plane at the interstitial site 1/2 1/2 0. The domain of δ values has been investigated by thermogravimetry, allowing to derive Tc versus δ without resorting to high oxygen pressures in the overdoped regime. We present both transverse and longitudinal magnetization measurements performed on a Hg1201 single crystal with an optimized Tc. We have extracted the penetration depth for in-plane currents λ//(0) and the anisotropy ratio γ.

We report dc magnetization measurements on the first available HgBa2CuO4+δ and HgBa2Ca2Cu3O8+δ (respectively Hg1201 and Hg1223) superconducting single crystals, for fields applied both perpendicular and parallel to the CuO2 planes. In the regime where the magnetization is reversible and linear in logarithm of the applied field, we have used the 3D London theory to determine the penetration depth λ ab for in-plane currents (λ ab (0)≃1300±100Å, for Hg1201 and ≈1500±100A for Hg1223). Using a relation derived from the anisotropic Ginzburg-Landau approach, we have made an estimate of the anisotropy factor (γ≈30 for Hg1201 and γ≈50 for Hg1223). The results are in agreement with recent torque experiments on Hg1223.

From torque measurements as a function of the angle and the magnetic field, we extract the magnetization curves and the anisotropy factor for a HgBa2Ca2Cu3O8+δ single crystal. The anisotropy is found γ = 52 ± 3; it is similar to the one found for the HgBa2Ca3Cu4O10+δ compound by Zech et al. The analysis of the magnetization close to Hc2(T) within the fluctuations theory yields the critical fluctuations parameter τf = (3.9 ± 0.4) 10−2 and the in-plane penetration depth λ(0) = 1500 ± 100 Å. The superconducting planes separation is found of the order of the unit cell length. The upper critical field is estimaated (dHc2dT)Tc0 ≈ 14 kOe K−1.

We have performed both longitudinal and transverse magnetization measurements on a HgBa2CuO4+δ single crystal, from which we extract the superconducting parameters (λ|(0) ≈ 1400 Å, ξ|(0) ≈ 20 Å). The anisotropy is found (γ ≈30) to be the lowest of the known values for the HgBa2Can−1CunO2n+2+δ family. A decrease of the apparent anisotropy is observed close to Tc, which we tentatively attribute to a quasi-2D to 3D crossover.

Polarized-light micro-Raman scattering (PLMRS) measurements have been performed on pre- and post-annealed Hg-1223 single crystals with Tc = 120 K and 135 K, respectively. Group-theoretical investigations, comparative analyses of the Hg-1223 structure to the Tl-1223 isomorphous one and arguments on electron-photon interaction have permitted us to identify the five Alg normal modes and defect for the first time the six Eg modes of the Hg-1223 system. No B1g mode has been observed.

X-ray diffraction analyses of good-quality single crystals of HgBa2Ca2Cu3O8+delta synthetized by a closed-vessel technique at low pressure, have lead to more definite results with respect to previous structural studies. Samples with T-c=135 K showed a Cu occupancy of 16.1% on the Hg site at the origin of the unit cell. Excess oxygen appears to be present only in the basal plane at the interstitial site 1/2, 1/2, 0 with an occupancy delta = 0.190 +/- 0.015. This compound has the shortest copper oxygen apical distance within the mercury family (2.696(3)Angstrom) together with an almost complete planarity of the CuO2 planes. Variations in the excess oxygen content upon different heat treatments were analyzed by thermogravimetry and magnetic-susceptibility measurements. A correlation between delta and T-c could be derived, showing in particular that superconductivity exists down to a very low interstitial oxygen content.

HgBa2Ca2Cu3O8+δ single crystals of submillimeter size were grown in a single-step synthesis under normal pressure. The crystals were examined by X-ray diffraction, energy dispersive X-ray analysis (EDX), scanning electron microscopy and magnetic measurements. The “as-grown” single crystals have a Tc of 120 K, as defined by the onset of diamagnetism. After annealing in oxygen at 300°C for 6 h, they can display a sharp superconducting transition temperature as high as 135 K.

We report the first measurements of the transport properties of single crystals of HgBa2Ca2Cu3O8+τ. Data for the in-plane and out-of-plane resistivity, in-plane Hall coefficient and in-plane thermoelectric power of single crystals with onset temperatures as high as 134 K are presented. The in-plane resistivity, Hall coefficient and thermoelectric power all indicate that these crystals are underdoped, which may offer at least a partial explanation for the strong pressure dependence of Tc observed in this compound. The in-plane Hall coefficient shows a strong temperature dependence in accord with other cuprate superconductors. A calculation of the cotangent of the Hall angle (cotθH) reveals that the relation cot θH=AT2 + B is obeyed to high precision in these crystals, despite strong curvature of the in-plane resistivity. Data are also reported for the influence of magnetic field on the resistive transition, for fields of up to 7 T applied both parallel and perpendicular to the crystallographic c-axis. These latter measurements give an estimate for the anisotropy of Hc2, implying a value which is intermediate between that found for YBa2Cu3O7−τ and Bi2Sr2CaCu2O8+x.

Well developed single crystals of the mercury compound HgBa2Ca2Cu3O8+δ have been obtained in single step synthesis under normal pressure conditions. Samples in the submillimeter range give a sizeable diamagnetic signal which allowed a systematic study of the magnetization anisotropy both before and after annealing in oxygen. After annealing, single crystals displayed a sharp superconducting transition temperature with an onset at 135 K. The direct determination by X-rays of the annealed crystal structure was carried out in addition to the analysis of the changes in the diffraction spectrum associated with the annealing process and the improvement of the transition temperature.

Superconducting single crystals of YBa2Cu3O7−δ displaying a secondary phase pattern superimposed on the orthorhombic bulk phase pattern have been investigated by X-ray diffraction. The crystal structure of the satellite phase material has been solved and shown to correspond to a new alkaline earth oxocuprate (II) BaCu3O4. It has orthorhombic symmetry. The space group is D192h-Cmmm with a=10.986Å, b=5.503Å, c=3.923Å and Z=2. All the oxygen atoms of the structure are involved in a 2-D network of copper-oxygen square planar coordination polyhedra having edge linkage. Short distances d(Cu-Cu)=2.752 Å are found along infinite 1-D copper chains. Structural similarities with YBa2Cu3O7−δ may explain the frequent occurence of BaCu3O4 within the host phase, and consequently its possible role as a weak link between superconducting regions.

The electrical conductivity (d.c. and 35 GHz) and thermopower of Fex[Pt(C2O4)2]·6H2O, FeOP, are presented and compared with those of other partially oxidized bis(oxalato)platinate salts of divalent cations. At room temperature FeOP is metallic with a conuctivity of 6 S cm−1 and a thermopower of 15 μV/K. Below room temperature there is a structural transition, which has little influence on transport properties. Below 160 K FeOP is a semiconductor with an activation energy of 55 meV.

Low-field (0.4 G⩽H⩽3 G) magnetization measurements have been performed on small single crystals of superconducting YBa2Cu3O7−δ (Tc⋍95 K) using a SQUID magnetometer. They revealed anisotropic properties in the temperature dependences of the shielding and the Meissner effects. A sharp unique transition at 95 K is observed with the field parallel to c. In the perpendicular direction a second transition line seems to be crossed at T∗=84 K. This temperature, T∗, decreases slightly as a function of the applied field in the range of fields investigated.

Low field (H ≤ 3G) magnetization measurements have been performed on small single crystals of superconducting YBa2Cu3O7-δ (Tc ≃ 95K) using a SQUID magnetometer. They revealed anisotropic properties in the temperature dependence of the magnetization. The Meissner effect (always smaller than 10 % ) is 2 to 3 times larger along the c direction than along one of the perpendicular directions. A sharp unique transition at 95K is observed with the field parallel to c. In the perpendicular direction a second transition line seems to be crossed at T = 84K with an applied field of 3G. In all three crystals studied, a very small ferromagnetic polarization, pointing approximately along the c direction, is observed.

An investigation into the variation of the intensity of the satellite reflections with temperature in Zn0.81[Pt(C2O4)2]·6H2O is reported. The first appearance of satellites corresponds to a big fall in conductivity and a large change in the thermopower, even though the intensity of the satellites is quite weak. The phase transition from Cccm to Pccn space group results in the appearance of new satellites and further large changes in both conductivity and thermopower.

A new periodic antiphase structure is proposed concerning the ordering of the counterions in the 1D Pt chain compounds Mx[Pt(C2O4)2]yH2O. Its diffraction spectrum, which is superimposed on the overall modulation spectrum previously described, is shown to be in agreement with the observed extinction rules. This type of ordering further supports the idea, introduced some years ago, postulating a fragmentation of these structures into periodic microdomains locally commensurate, but statistically incommensurate with the underlying lattice.