A novel cubic perovskite MnCu3V4O12 has been synthesized at a high pressure and high temperature of 12 GPa and 1373 K. This compound crystallizes in the A-site-ordered perovskite structure (space group Im3) with lattice constant a = 7.26684(10) Å at room temperature. The most notable feature of this compound lies in the fact that the Mn(2+) ion is surrounded by 12 equidistant oxide ions to form a regular icosahedron; the situation of Mn(2+) is unprecedented for the crystal chemistry of an oxide. An anomalously large atomic displacement parameter U(iso)= 0.0222(8) Å(2) is found for Mn(2+) at room temperature, indicating that the thermal oscillation of the small Mn(2+) ion in a large icosahedron is fairly active. Magnetic susceptibility and electric resistivity measurements reveal that 3d electrons of Mn(2+) ions are mainly localized, while 3d electrons in Cu(2+) and V(4+) ions are delocalized and contribute to the metallic conduction.

Of particular interest is a peculiar motion of guest atoms or ions confined to nanospace in cage compounds, called rattling. While rattling provides unexplored physical properties through the guest-host interactions, it has only been observed in a very limited class of materials. Herein, we introduce an A-site-ordered quadruple perovskite, CuCu3 V4 O12 , as a new family of cage compounds. This novel AA'3 B4 O12 -type perovskite has been obtained by a high-pressure synthesis technique and structurally characterized to have cubic Im$\bar 3$ symmetry with an ionic model of Cu(2+) Cu(2+) 3 V(4+) 4 O12 . The thermal displacement parameter of the A-site Cu(2+) ion is as large as Uiso ≈0.045 Å(2) at 300 K, indicating its large-amplitude thermal oscillations in the oversized icosahedral cages. Remarkably, the presence of localized phonon modes associated with rattling of the A-site Cu(2+) ion manifests itself in the low-temperature specific heat data. This work sheds new light on the structure-property relations in perovskites.

Of particular interest is ap eculiar motion of guest atoms or ions confined to nanospace in cage compounds, called rattling.W hile rattling provides unexplored physical properties through the guest-host interactions,ithas only been observed in av ery limited class of materials.H erein, we introduce an A-site-ordered quadruple perovskite, CuCu 3 V 4 O 12 ,a sanew family of cage compounds.T his novel AA' 3 B 4 O 12 -type perovskite has been obtained by ah ighpressure synthesis technique and structurally characterized to have cubic Im3 symmetry with an ionic model of Cu 2+ Cu 2+ 3 V 4+ 4 O 12 .T he thermal displacement parameter of the A-site Cu 2+ ion is as large as U iso % 0.045 2 at 300 K, indicating its large-amplitude thermal oscillations in the oversized icosahedral cages.R emarkably,t he presence of localized phonon modes associated with rattling of the A-site Cu 2+ ion manifests itself in the low-temperature specific heat data. This work sheds new light on the structure-property relations in perovskites.

A novel silver-containing perovskite, AgCu3V4O12, was synthesized under high-pressure and high-temperature conditions. It crystallizes in an A-site-ordered perovskite structure (space group Im3), in which silver ions occupy the 12-coordinated A sites forming regular icosahedra, and exhibits metallic behavior. Bond-valence-sum calculations and X-ray photoemission spectroscopy reveal that Ag ions are present in the mixed-valence state, most likely attributable to the coexistence of Ag(+) and Ag(3+), unlike the case of well-known perovskite-type AgNbO3 and AgTaO3 containing only Ag(+) ions. We discuss metallic conduction in relation to electronic structure calculations.

Rattling in the Quadruple Perovskite CuCu 3V4O12. -A new A-site-ordered quadruple perovskite CuCu 3V4O12 is obtained by a high-pressure solid state reaction of a 2:12:3:5 molar mixture of Cu 2O, CuO, V2O3, and V2O5, resp. (Pt capsule in high-pressure cell, 15 GPa 1523 K, 30 min). The compound crystallizes in the cubic space group Im3 (synchrotron powder XRD) with an ionic model of Cu 2+ O12. The thermal displacement parameter of the A-site Cu 2+ ion is 0.045 Å 2 at 300 K indicating its large-amplitude thermal oscillations in the oversized icosahedral cages. The presence of localized phonon modes associated with rattling of the A-site Cu 2+ ion manifests itself in the low-temperature specific heat data. -(AKIZUKI, Y.; YAMADA*, I.; FUJITA, K.; TAGA, K.; KAWAKAMI, T.; MIZUMAKI, M.; TANAKA, K.; Angew.