Synthesis, Structure, and Ferromagnetism of a New Oxygen Defect Pyrochlore System Lu2V2O_{7-x} (x = 0.40-0.65)

A new fcc oxygen defect pyrochlore structure system Lu2V2O_{7-x} with x = 0.40 to 0.65 was synthesized from the known fcc ferromagnetic semiconductor pyrochlore compound Lu2V2O7 which can be written as Lu2V2O6O' with two inequivalent oxygen sites O and O'. Rietveld x-ray diffraction refinements showed significant Lu-V antisite disorder for x >= 0.5. The lattice parameter versus x (including x = 0) shows a distinct maximum at x ~ 0.4. We propose that these observations can be explained if the oxygen defects are on the O' sublattice of the structure. The magnetic susceptibility versus temperature exhibits Curie-Weiss behavior above 150 K for all x, with a Curie constant C that increases with x as expected in an ionic model. However, the magnetization measurements also show that the (ferromagnetic) Weiss temperature theta and the ferromagnetic ordering temperature T_C both strongly decrease with increasing x instead of increasing as expected from C(x). The T_C decreases from 73 K for x = 0 to 21 K for x = 0.65. Furthermore, the saturation moment at a field of 5.5 T at 5 K is nearly independent of x, with the value expected for a fixed spin 1/2 per V. The latter three observations suggest that Lu2V2O_{7-x} may contain localized spin 1/2 vanadium moments in a metallic background that is induced by oxygen defect doping, instead of being a semiconductor as suggested by the C(x) dependence.Comment: 9 pages including 7 figures, 3 table

Phase chemistry in the Ca-Mn-Sb-O system at 1160-1250 °C

Phase equilibrium in the Ca-Mn-Sb-O system was studied in air at the temperature range from 1160 to 1250°C and a pseudo-quaternary phase diagram for the system CaO-MnO-Mn2O3-Sb2O5 is presented. The following compounds were discovered: new antimonate Ca 7Sb2O12 with a perovskite-like structure, solid solutions Mn2-xCaxSb2O7 (0 ≤ x ≤ 1.6) with a 3T-weberite structure, and Ca2-xMn xSb2O7 (0 ≤ x ≤ 0.23) with a 2O-weberite structure, as well as solid solutions Ca2Mn1+xSb 1-xO6 with monoclinic (0 ≤ x ≤ 0.67) and orthorhombic (0.75 ≤ x ≤ 1) perovskite structures. The existence of a number of double and ternary oxides and solid solutions on the basis of Sb 5+ and Mn2+, Mn3+, Mn4+ and with mixed manganese valence is confirmed. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Stability of geometrically frustrated magnetic state of Ca3CoRhO6 to applications of positive and negative pressure

The influence of negative chemical pressure induced by gradual replacement of Ca by Sr as well as of external pressure (up to 10 kbar) on the magnetism of Ca3CoRhO6 has been investigated by magnetization studies. It is found that the solid solution, Ca(3-x)Sr(x)CoRhO6, exists at least till about x= 1.0 without any change in the crystal structure. Apart from insensitivity of the spin-chain feature to volume expansion, the characteristic features of geometrical frustration interestingly appear at the same temperatures for all compositions, in sharp contrast to the response to Y substitution for Ca (reported previously). Interestingly, huge frequency dependence of ac susceptibility known for the parent compound persists for all compositions. We do not find a change in the properties under external pressure. The stability of the magnetic anomalies of this compound to the volume change (about 4%) is puzzling

Investigation of the magnetic phase transition and magnetocaloric properties of the Mn2_2FeSbO6_6 ilmenite

The magnetic phase transition and magnetocaloric properties of mineral and synthetic melanostibite Mn$_2$FeSbO$_6$ with ilmenite-type structure have been studied. Mn$_2$FeSbO$_6$ orders ferrimagnetically below 270 K and is found to undergo a second-order magnetic phase transition. The associated magnetic entropy change amounts to 1.7 J/kgK for the mineral and 1.8 J/kgK synthetic melanostibite for 5 T field change. For the synthetic Mn$_2$FeSbO$_6$ the adiabatic temperature change was estimated from magnetic- and specific heat measurements and amounts to 0.2 K in 1 T field change. Perspectives of the promising functional properties of Mn$_2$FeSbO$_6$-based materials are discussed.Comment: 6 pages, 7 figure

Synthesis and crystal structure of a new hexagonal perovskite 7H-Ba7Li1.75Mn3.5O15.75 with Mn4+/Mn5+ charge distribution.

Our work describes the synthesis and crystal structure of a new hexagonal perovskite 7H-Ba7Li1.75Mn3.5O15.75with Mn4+/Mn5+charge distribution.</p

Correction: Synthesis and crystal structure of a new hexagonal perovskite 7H-Ba7Li1.75Mn3.5O15.75 with Mn4+/Mn5+ charge distribution.

The authors regret a spelling mistake in the surname of one of authors. The surname given as ‘Vasilev’ should be ‘Vasiliev’. Furthermore a second affiliation for the author A. D. Vasiliev was inadvertently omitted. The correct spelling and affiliations of all the authors for this paper is as shown above. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers

Seebeck coefficient of a quantum confined, high-electron-density electron gas in SrTiO 3

We report on the Seebeck coefficient of quantum confined electron gases in GdTiO3/SrTiO3heterostructures. These structures contain two-dimensional electron gases with very highsheet-carrier concentrations on the SrTiO3-side of the interface due to intrinsic interface doping.While the sheet carrier concentrations are independent of the thickness of the SrTiO3layer, theSeebeck coefficient initially increases with SrTiO3thickness before saturating at a value of300 lK/V. A model of the Seebeck coefficient, based on thermally populated, self-consistent,tight binding subbands, captures in a semi-quantitative manner the observed thickness dependence