Single crystal growth of spin ladders and related compounds at high pressure.

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High pressure (HP) synthesis is a powerful technique to search for new materials. We have discovered many low dimensional magnets such as high-T_c superconductors and spin ladder compounds using this technique. Generally speaking, however, it used to be almost impossible to obtain single crystal samples of these high-pressure phases because of the lack of the information about the HP-HT (high temperature) reactions. High energy, high flux X-ray from synchrotron radiation enabled us to observe such a reaction in a HP cell even if the sample is in a gold or a platinum capsule. The melting point of the samples with various kinds of flux were determined and such information was applied for the single crystal growth.1. HP phase of (VO)_2P_2O_7 : S =1/2 one dimensional alternating exchange antiferromagnet with a spin gap. The powder XRD data collected with a cubic-anvil type high-pressure apparatus installed at BL14B1 of Spring-8 clearly showed the transformation from the AP phase to the HP … More phase at 3GPa and 500゜C and the melting at 1150゜C.Single crystals were obtained by slowly cooling the melt from 1300゜C to 700゜C in 60h at 3GPa using a in-house HP apparatus.2. Ca_<2-x>Na_xCuO_2Cl_2 : High Tc superconductor with chlorine instead of apical oxygen. It is an ideal compound for photoemission and STM measurements because a) easy to cleave (fresh CuO_2 plane is available), b) samples from insulator to doped superconductor are available, c) there is no orthorhombic distortion at low temperature, d)it has no modulation. Mixtures of Ca_2CuO_2Cl_2, NaClO_4 and NaCl were slowly cooled from 1250゜C to 1050゜C at various pressures to obtain plate-like crystals. NaClO_4 worked as flux, Na source and oxygen generator. The Na content could be tuned by changing the pressure during the crystal growth.3. CaFeO_3 : a distorted perovskite (GdFeO_3 type) with unusual Fe^<4+> ion which shows charge disproportionation to Fe^<3+> and Fe^<5+> below room temperature. A mixture of KClO_4, NaClO_4 and CaCl_2 was used as flux and oxygen generator. Less