A-site ordered perovskite CaCu3Cu2Ir2O(12-δ) with square-planar and octahedral coordinated Cu ions

A novel CaCu_3Cu_2Ir_2O_（12-δ） polycrystalline sample was synthesized at 8 GPa and 1373 K.Rietveld structural analysis shows that this compound crystallizes in an AA＇_3B_4O_（12）-type A-site ordered perovskite structure with space group Im-3.Xray absorption spectra reveal a ＋2-charge state for both the square-planar and octahedral coordinated Cu ions,and the valence state of Ir is found to be about ＋5.Although the A-site Ca and the A＇-site Cu^（2＋） are 1：3 ordered at fixed atomic positions,the distribution of B-site Cu^（2＋） and Ir^（5＋） is disorderly.As a result,no long-range magnetic ordering is observed at temperatures down to 2 K.Electrical transport and heat capacity measurements demonstrate itinerant electronic behavior.The crystal structure is stable with pressure up to 35.7 GPa at room temperature.

A-site ordered quadruple perovskite oxides AA＇_3B_4O_(12)

The A-site ordered perovskite oxides with chemical formula AA＇3B4O（12）display many intriguing physical properties due to the introduction of transition metals at both A and B sites. Here, research on the recently discovered intermetallic charge transfer occurring between A-site Cu and B-site Fe ions in La Cu3Fe4O（12） and its analogues is reviewed, along with work on the magnetoelectric multiferroicity observed in La Mn3Cr4O（12） with cubic perovskite structure. The Cu–Fe intermetallic charge transfer（LaCu3（3＋）Fe4（3＋）O（12）→ LaCu3（2＋）Fe4（3.75＋）O（12）） leads to a first-order isostructural phase transition accompanied by drastic variations in magnetism and electrical transport properties. The La Mn3Cr4O（12） is a novel spindriven multiferroic system with strong magnetoelectric coupling effects. The compound is the first example of cubic perovskite multiferroics to be found. It opens up a new arena for studying unexpected multiferroic mechanisms.

Effect of Quench Treatment on Fe/Mo Order and Magnetic Properties of Double Perovskite Sr_2FeMoO_6

A quench-treatment technique is used to prepare a high-quality polycrystalline sample of double perovskite Sr2FeMo06 （SFMO）. X-ray powder diffraction analysis reveals that the sample has a single phase and exhibits I4/m symmetry. The cation order η of the sample increases to 98.9（2）% from 94.2（3）%, which is prepared by the traditional sol-gel method. The initial magnetization isotherm of the sample is detected at 300 K. Unit-cell magnetization for the current sample is 1.332 #s at 300 K, and the one for the traditional sol-gel method sample is 0.946#9. Unit-cell magnetization is enhanced to 40.80% by the quench-treatment technique. Quench treatment is an effective method of enhancing the Fe/Mo order and magnetic properties of double perovskite SFMO.

Effect of anionic ordering on the electronic and optical properties of BaTaO2N：TB-mBJ density functional calculation

This report presents a first-principles investigation of the structural, electronic, and optical properties of perovskite oxynitrides BaTaO2 N by means of density functional theory（DFT） calculations using the full-potential linearized augmented plane wave（FP-LAPW） method. Three possible structures（P4mm, I4/mmm, and Pmma） are considered according to the TaO4N2 octahedral configurations. The calculated structural parameters are found to be in good agreement with the previous theoretical and experimental results. Moreover, the electronic band structure dispersion, total, and partial densities of electron states are investigated to explain the origin of bandgaps and the contribution of each orbital＇s species in the valence and the conduction bands. The calculated minimum bandgaps of the P4 mm, I4/mmm, and Pmma structures are 1.83 e V, 1.59 e V, and 1.49 e V, respectively. Furthermore, the optical properties represented by the dielectric functions calculated for BaTaO2 N show that the I4/mmm phase absorbs the light at a large window in both the visible and UV regions,whereas the other two structures（P4mm and Pmma） are more active in the UV region. Our investigations provide important information for the potential application of this material.