Possible Verwey-Type Transition in Pb₃Rh₇O₁₅

Abstract

Crystals of the mixed-valence compound Pb3Rh4 3+Rh3 4+O15 have been grown in a PbO flux. These hexagonal crystals show an isotropic electrical resistivity of about 1 × 10−3 ohm cm at room temperature. This resistivity slowly increases with decreasing temperature until 185 K, where the resistivity begins increasing more rapidly as temperature is further decreased. Specific heat measurements on polycrystalline Pb3Rh7O15 show a sharp, lambda-shaped peak at 185 K. Magnetic susceptibility and thermopower measurements on Pb3Rh7O15 also show a discontinuity at about 185 K. Structural analyses of X-ray diffraction data obtained above and below 185 K indicate that a change in space group has occurred at 185 K. It is likely that the transition at 185 K is related to a change in charge modulation. The phase transition at 185 K fades away as Bi is substituted for Pb in Pb3Rh7O15.

A new rare-earth oxyborate Ba3BiPbEuO(BO3)4and the luminescence properties of the Ba3BiPbY1−xEuxO(BO3)4phosphors

“…1.19 Å for Pb 2+ , CN = 6) and coordination geometries. 30 The Bi 3+ /Pb 2+ disorder has also been previously reported in other crystal structures, such as Pb 2.04 Bi 0.96 Rh 7 O 15 , 31 Pb 3 BiV 3 O 12 , 32 and (Bi 0.2 Pb 0.8 )(Fe 0.2 Zr 0.8 )O 3 . 33 Furthermore, the structure was checked by the program PLATON 34 and no additional symmetries were detected.…”

CsTe2O6–x: Novel Mixed-Valence Tellurium Oxides with Framework-Deficient Pyrochlore-Related Structure

“…This is common behavior for lone pair cations. Close proximity of lone pairs occurs in PbO as well as in ternary oxides of Pb 2+ . , This behavior is also well known in ternary oxides of Te 4+ , with CaTeO 3 being a particularly good example . In CsTe 2 O 5.75 there are not enough O vacancies to accommodate all the Te 4+ in positions adjacent to an O vacancy.…”

Synthesis and crystal structure of two new cerium rhodium oxides: Ce2/3−xRh3+2O4 (x∼0.12) with Ce mixed valency and Ce4+Rh3+2O5

“…The bond valence sums for Rh and Ce were calculated to be 3.19 and 3.82, respectively, suggesting the formula Ce 4 þ Rh 3 þ 2 O 5 . We used a bond valence parameter, l 0 ¼1.800 for Rh 3 þ , which was deduced recently [11]. A notable feature of the CeRh 2 O 5 structure is the zigzag chains of edgeshared Rh octahedra extending along the c-axis.…”