Mn₂(Fe_0.8Mo_0.2)MoO₆: A Double Perovskite with Multiple Transition Metal Sublattice Magnetic Effects

Transition-metal-only perovskite oxides can introduce additional magnetic functionality with robust magnetoelectric properties but are rare. In this work we prepared a new transition-metal-only perovskite Mn₂(Fe_0.8Mo_0.2)­MoO₆ at high pressure and temperature. Uniquely, Mn₂(Fe_0.8Mo_0.2)­MoO₆ was discovered as a line phase upon composition modulation that was motivated from the above-room-temperature multiferroic Mn₂FeMoO₆ corundum phase. It exhibits ferrimagnetic Fe–Mo sublattice (<i>T</i>_C = 194 K) and Mn sublattice antiferromagnetic (<i>T</i>_m ∼ 45 K) transitions. Below <i>T</i>_m the two sublattice orderings are coupled and give rise to canted components in both. A first-order field-induced transition is also observed below 45 K. Mn₂(Fe_0.8Mo_0.2)­MoO₆ is a Mott variable range hopping semiconductor. These findings for the first time show that either an exotic perovskite or a corundum phase can be achieved by composition modulation besides the pressure effect

Synthesis, Structure, and Properties of the Layered Oxyselenide Ba₂CuO₂Cu₂Se₂

A new layered oxyselenide, Ba₂CuO₂Cu₂Se₂, was synthesized under high-pressure and high-temperature conditions and was characterized via structural, magnetic, and transport measurements. It crystallizes into space group <i>I</i>4/<i>mmm</i> and consists of a square lattice of [CuO₂] planes and antifluorite-type [Cu₂Se₂] layers, which are alternately stacked along the <i>c</i> axis. The lattice parameters are obtained as <i>a</i> = <i>b</i> = 4.0885 Å and <i>c</i> = 19.6887 Å. The Cu–O bond length is given by half of the lattice constant <i>a</i>, i.e., 2.0443 Å. Ba₂CuO₂Cu₂Se₂ is a semiconductor with a resistivity of ∼18 mΩ·cm at room temperature. No magnetic transition was found in the measured temperature range, and the Curie–Weiss temperature was obtained as −0.2 K, suggesting a very weak exchange interaction. The DFT+<i>U</i>_eff calculation demonstrates that the band gap is about 0.2 eV for the supposed antiferromagnetic order, and the density of state near the top of the valence band is mainly contributed from the Se 4p electrons

A‑Site and B‑Site Charge Orderings in an <i>s–d</i> Level Controlled Perovskite Oxide PbCoO₃

Perovskite PbCoO₃ synthesized at 12 GPa was found to have an unusual charge distribution of Pb²⁺Pb⁴⁺₃Co²⁺₂Co³⁺₂O₁₂ with charge orderings in both the A and B sites of perovskite ABO₃. Comprehensive studies using density functional theory (DFT) calculation, electron diffraction (ED), synchrotron X-ray diffraction (SXRD), neutron powder diffraction (NPD), hard X-ray photoemission spectroscopy (HAXPES), soft X-ray absorption spectroscopy (XAS), and measurements of specific heat as well as magnetic and electrical properties provide evidence of lead ion and cobalt ion charge ordering leading to Pb²⁺Pb⁴⁺₃Co²⁺₂Co³⁺₂O₁₂ quadruple perovskite structure. It is shown that the average valence distribution of Pb^3.5+Co^2.5+O₃ between Pb³⁺Cr³⁺O₃ and Pb⁴⁺Ni²⁺O₃ can be stabilized by tuning the energy levels of Pb 6<i>s</i> and transition metal 3<i>d</i> orbitals