J.P. Hodges

Superconductivity up to 64 K in the copper oxyfluorides Sr2−xAxCuO2F2+δ(A = Ca, Ba) prepared using NH4F as a fluorinating reagent

Abstract We report here a simple and efficient synthetic route to high-temperature superconducting oxyfluorides. Solid phase fluorination of Sr 2 CuO 3 with NH 4 F at relatively low temperatures produces superconducting Sr 2 CuO 2 F 2+δ ; this simple preparation route eliminates the need for F 2 gas. Importantly, as-synthesised samples from the NH 4 F route appear to have the optimally doped value of the superconducting transition temperature, T c , of 46 K. Moreover, Ba doping for Sr results in an increase in T c , for both F 2 gas and NH 4 F routes, to a maximum value of 64 K for Sr 1.4 Ba 0.6 CuO 2 F 2+δ ; this represents the highest ever recorded value for a material with the confirmed La 2 CuO 4 structure.

An improved route to the synthesis of superconducting copper oxyfluorides Sr2−xAxCuO2F2+δ (ACa, Ba) using transition metal difluorides as fluorinating reagents

Abstract We report here a simple and efficient synthetic route to high temperature superconducting oxyfluorides. Solid phase fluorination of Sr 2− x A x CuO 3 (Aue5fbCa, 0 ⩽ x ⩽ 2.0; Aue5fbBa, 0 ⩽ x ⩽ 0.6) with the transition metal difluorides, CuF 2 , ZnF 2 , AgF 2 , NiF 2 , at relatively low temperatures (225–250°C) produces superconducting Sr 2− x A x CuO 2 F 2+δ with a maximum T c of 64 K (for Aue5fbBa, x = 0.6). This simple preparation route eliminates the need for F 2 gas, and at the same time produces negligible (Sr/A)F 2 impurity, unlike the corresponding fluorination with NH 4 F. Using this route the synthesis of the oxyfluoride, Ba 2 CuO 2 F 2+δ , is also reported for the first time. These studies and the examination of the fluorination of other cuprate systems have shown that this is a powerful and versatile fluorination route.

Observation of superconductivity (Tc = 50 K) in a new tetragonal alkaline-earth cuprate Sr0.8Ba1.2CuO3+δ, synthesised at ambient pressure

Abstract The ambient-pressure synthesis of a new tetragonal alkaline-earth superconducting cuprate, Sr0.8Ba1.2CuO3+δ, from a cupro-oxycarbonate is reported. Magnetic-susceptibility measurements show the presence of a superconducting transition ∼50 K in a post-annealed sample. The crystal structure, refined from time-of-flight powder neutron-diffraction data was found to have an oxygen-deficient La2CuO4-type tetragonal T structure ( a = 3.8988(3) A and c = 12.815(3) A ) with oxygen vacancies located within the CuO2 planes. Ordering of these oxygen vacancies is responsible for the observation of a superlattice in both neutron- and electron-diffraction measurements. An interpretation of the electron-diffraction patterns suggests that the superlattice in Sr0.8Ba1.2CuO3+δ and also in the isostructural superconductor Sr2CuO3+δ are of an identical nature.

Mercurocuprates: The Highest Transition-Temperature Superconductors

With these words [1] Heike Kamerlingh-Onnes summarised the existence of “a new state” of mercury. This discovery (initially made in 1911 [2]) gave the world the first superconductor — elemental mercury — which entered this new state of matter below a superconducting transition temperature (Tc) of 4.2K. Eight decades later, mercury once again took centre stage, but this time in a chemically combined state, as the [O-Hg-O]2- unitwithin a mixed-metal oxide possessing superconductivity up to a record-high temperature of some 133K.

Issues involved in the synthesis if mercury containing superconductors

Abstract The recently discovered homologous series HgBa 2 Ca n−1 Cu n O 2n+2+δ includes the highest superconducting transition temperature known. The preparation of these materials provides a continuing challenge to the synthetic solid-state chemist; pure or nearly pure samples are still proving elusive. We have investigated a variety of preparative routes and report here our findings on the appropriateness and optimisation of synthetic conditions. The materials have been prepared both from precursors and in single-stage reactions, using a variety of both solid and aqueous starting materials. All mercurations have been carried out under controlled atmospheres, using sealed reaction vessels. Preparation of thin-films of these superconductors has also been studied using the complimentary synthetic technique of laser ablation.