High-Pressure Stabilization of New Transition Metal Oxides with the Perovskite Structure and Their Physical Properties

高压合成已被用于稳定具有钙钛矿结构的新型过渡金属氧化物，从而获得诸如铁磁性和超导性等有趣的物理性质。在4gpa和600℃的温度下合成了含t_c105k的铁磁体BiMnO_3。Sr取代Bi大大降低了电阻率，但没有实现金属态，不像金属，铁磁体（La, Sr）MnO_3。磁矩随Sr浓度的增加而减小，在Sr浓度为40%左右，铁磁性完全消失。用中子衍射法测定了单临床畸变钙钛矿的晶体结构。利用Rietveld分析对粉末结构进行细化，发现由于Bi^<3+>离子的6s2孤对极化，Bi原子明显偏离规则的12配位位。每一个Mn^<3+ b>离子都表现出姜-泰勒扭曲。相邻Mn^<3+>离子之间的超交换相互作用预计为2/3为平行，1/3为反平行，因此认为铁磁相互作用占主导地位。与LaMnO_3不同的是，相对均匀的空dx_<2-y2>轨道的分布可以解释BiMnO_3的铁磁性。在1.5 ~ 2.5 gpa和1000℃左右的温度下，进行了ti基铜酸盐的高压合成。制备了T_c分别为97K和90K的TlSr_2Ca_2Cu_3O_y和TlSr_2Ca_3Cu4O_<yp>高Tc氧化物。认为高压条件有利于防止钛在长时间退火过程中的蒸发，这是建立Ca和sr有序排列所必需的，并尝试了冲击合成高Tc铜酸盐。通过冲击载荷成功合成了cla= 3.0的EuBa_2Cu_2O_<6.5>的正方EuBa_2Cu_2O_，但经氧处理未实现超导性。在900℃以上的温度下，以冲击方式合成的产物才会出现超导现象，并在Eu和Ba之间建立了完美的顺序。

High pressure synthesis has been utilized to stabilize new transition metal oxides with the perovskite structure, thereby achieving interesting physical properties like ferromagnetism and superconductivity. A ferro-magnet BiMnO_3 with T_cof 105K was synthesized at 4 GPa and 600ﾟC.Sr substitution for Bi reduces electrical resistivity considerably, but no metallic states were realized, unlike metallic, ferromagnet (La, Sr)MnO_3. Magnetic moment rather decreased with increasing Sr concentration and ferromagnetism completely disappeared around 40% Sr concentration.Crystal structure of monoclinically distorted perovskite was determined by neutron diffraction. Structure refinement using Rietveld analysis of powder pattern revealed that the Bi atom deviated remarkably from regular 12-coordinated sites owing to polarized 6s2 lone pair of Bi^<3+> ions. Every Mn^<3+> ions showed Jahn-Teller distortion. Superexchange interaction between adjacent Mn^<3+> ions were expected to be parallel for 2/3 and anti-parallel for 1/3, hence ferromagnetic interactions were considered to be dominated. Unlike LaMnO_3, rather homogeneous distribution of vacant dx_<2-y2> orbitals would explain the ferromagnetism of BiMnO_3.High pressure synthesis of TI-based cuprates was carried out for 1 .5-2.5GPa and around 1000ﾟC.New high Tc oxides of TlSr_2Ca_2Cu_3O_y and TlSr_2Ca_3Cu4O_<yp> wiht T_c of 97K and 90K were obtained. High pressure condition was considered to be favorable for preventing TI evaporation in long time annealing which was necessary for establishing ordered arrangement of Ca and Sr.Shock synthesis of high Tc cuprates was also tried. Tetragonal EuBa_2Cu_2O_<6.5> with cla= 3.0 was successfully synthesized by shock loading of the component mixture, but no superconductivity was realized by oxygen treatment. Superconductivity appeared only after annealing the as-shock-synthesized product above 900ﾟC, which established perfect order among Eu and Ba.