Frist-principle Studies Of4d Perovskite ATcO₃（A=Ca,Sr,Ba）

Materials with perovskite structure have attracted great interest because of the peculi-ar physics and the potential value to design novel devices for applications. In recent years,the4d transition-metal oxides have been widely studied from researches. However, sincetechnetium (Tc) decays by β-emission, its solid state chemistry and physics have not beenwidely studied until CaTcO3and SrTcO3were synthesized successfully in2011and the TNsreach surprisingly high values of800K and1023K, respectively. By using first-principlemethods, the structural, magnetic and electronic properties of4d high Neel temperatureperovskite ATcO3(A=Ca, Sr, Ba) have been studied with the generalized gradient ap-proximation (GGA) plus on-site Coulomb interaction corrections (GGA+U) method.CaTcO3and SrTcO3are found to be insulators with G-type antiferromagnetic ordering andlarge superexchange interactions with Pnma symmetry. For BaTcO3which is not synthe-sized so far, a range of possible crystal structures is examined and the energetically favora-ble structure is the six-layered hexagonal structure P63/mmc with antiferromagnetic cou-pling both within the Tc2O9entities and between the Tc ions in the corner-sharing octahe-dral. We predict the Neel temperature of BaTcO3is about1007K.