High oxygen pressure single crystal growth of highly Ca-doped spin ladder compound Sr14−xCaxCu24O41 (x>12)

Large size high-quality Ca-doped Sr14−xCaxCu24O41 (x=12.2, 12.6 and 13) spin ladder superconducting single crystals were grown using a modified mirror floating zone furnace with oxygen pressure up to 35 bar. The qualities of the as-grown single crystals were confirmed by polarized optical microscopy, neutron diffraction and X-ray diffraction methods. The sample compositions and homogeneity were measured using micro-X-ray fluorescence spectroscopy. The lattice parameters of each sample have been refined using the Rietveld method. The oxygen stoichiometry measurements which were performed by hydrogen reduction/thermogravimetry method show that all the three samples are slightly oxygen deficient even though high oxygen pressure was applied during growth. The high oxygen pressure is indispensible for growing highly Ca-doped Sr14−xCaxCu24O41 single crystals. The susceptibility was measured along c-axis for all three compositions, fitting well with the one dimensional dimer model, consistent with the reported values of undoped Sr14Cu24O41 parent compounds.

▶ High pressure (up to 35 bar) traveling solvent floating zone furnace. ▶ Large size highly Ca-doped (x=12.2, 12.6 and 13) Sr14−xCaxCu24O41 single crystals were grown. ▶ High crystal quality and homogeneity confirmed by neutron diffraction and Micro-XRF. ▶ Incommensurate structural refinement with superspace group Xmmm(0 0 γ)ss0.