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Résumé |
Pressures of ≤10GPa are not so high but are very interesting from the viewpoint of synthesis: In this pressure range almost all substances show nonlinearity in the pressure dependence of specific volume, which is a sign of instability and a sign of the susceptibility to perturbations being enhanced. My group has obtained rare Fe4+-oxides like CaFeO3, two-legged and three-legged cupric spin ladder oxides like SrCu2O3, (La,Sr)CuO2.5, and Sr2Cu3O5, cupric-oxide superconductors like Ca2-xNaxCuO2Cl2 and Ca2-x□xCuO2Cl2, ferromagnetic ferroelectrics like Bi2MnNiO6, SrCo6O11 showing a specific two-staged magnetoresistance, and BiNiO3 showing an unprecedented A-site charge disproportionantion expressed as Bi3+0.5Bi5+0.5Ni2+O3 (triclinic, insulator) and a pressure-induced inter-site charge transfer leading to Bi3+Ni3+O3 (P>4GPa, orthorhombic, metal). The efficiency of crystal growth under HP has been greatly improved since it has become possible to directly observe what goes on in a sample cell by using powerful XRD.
SrTiO3 which is made metallic by introducing oxygen deficiency or by the La3+-for-Sr2+ substitution has been found to show photoluminescence and cathode luminescence centered at 430nm (blue) at room temperature. Ar ion irradiation is a way to generate oxygen deficiency in the surface of a crystal, and by making use of a photolithographic technique the Ar-irradiated and, therefore, luminescent and metallic region can be patterned.
Thanks to its very strong magnetic anisotropy nano-sized particles of the fct phase of FePt, in which the Fe and the Pt are ordered along the c-axis, may serve as a magnetic memory of an ultrahigh density of ≥1Tb/in2. A method to prepare monodisperse and magnetically superior nanoparticles that are dispersible in nonpolar organic solvents such as hexane has been developed.
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