Yellow pyroantimonates PbSb, PbSbSn and PbSbZn were synthesized by solid-state reactions at high temperature and characterized by X-ray diffraction and Raman spectroscopy. The lattice size of cubic pyrochlores increases with Sn and Zn doping and with Pb overstoichiometry, indicating the replacement of Sb5+ by the larger cations. This fact permits the understanding of the corresponding Raman spectral modifications as a consequence of the changes in the local symmetry of the SbO polyhedra, justifying the exploitation of Raman spectroscopy to noninvasively identify structural modifications of pyroantimonate pigments in artworks. Copyright © 2008 John Wiley & Sons, Ltd.

Raman scattering features of lead pyroantimonate compounds. Part I: XRD and Raman characterization of Pb2Sb2O7 doped with tin and zinc

Nickel titanate nanofibers by electrospinning

Investigations on the temperature dependent electrical and magnetic properties of NiTiO3 by molten salt synthesis

A modified mixed oxide synthetic route has been developed for the synthesis of the columbite-like phase of magnesium niobate, MgNb 2 O 6 (MN). Magnesium carbonate hydroxide pentahydrate was employed as a source of magnesium, with the formation of columbite phase investigated as a function of calcination temperature and dwell time by XRD and DTA. The particle size distribution of the calcined powder was determined by laser diffraction, with the morphology, phase composition and crystal structure determined via SEM, TEM and EDX techniques. It has been found that the Mg 4 Nb 2 O 9 phase tends to form together with the columbite-type phase MgNb 2 O 6 , although a single columbite-like phase of MgNb 2 O 6 was obtained for a calcination temperature of 1150°C with a dwell-time of 4 h. ©

Synthesis, formation and characterisation of MgNb2O6 powder in a columbite-like phase

Synthesis and Characterization of Tin Niobates

Formation of lead magnesium niobate (PMN) perovskite phase using a columbite type of precursor together with the addition of excess MgO has been investigated When MgO and Nb2O5 are reacted with 1:1 stoichiometry, a minor amount (}2%) of Mg4Nb2O9 is formed along with the columbite-type phase which in turn could lead to the formation of a minor amount of “free Nb2O5” in the precursor This may be the reason for the formation of small amounts of pyrochlore phase during the synthesis of PMN perovskite from the stoichiometric 1:1 precursor However, it has been found that the perovskite phase can easily be stabilized by the addition of a large excess of MgO in the precursor, although this leads to additional Mg-Nb-O phase Mg4Nb2O9, besides the columbite-type phase MgNb2O6 It has been shown that, after this precursor reacts with PbO to form the PMN perovskite, the excess Mg present in the Mg-rich niobate precursor separates out as MgO, as evidenced by X-ray diffraction, which can be removed by leaching with dilute nitric acid, thus forming pure PMN

Formation of Lead Magnesium Niobate Perovskite from Niobate Precursors Having Varying Magnesium Content

Synthesis of lead tantalate pyrochlores by the reaction of PbO and Ta2O5 in various molar ratios between 1.5 and 4.0 at low temperatures (500–650°C) has been carried out. It has been shown that when PbO is reacted with Ta2O5 in various molar ratios at low temperatures, metastable lead tantalate pyrochlore solid solutions having cubic symmetry are formed. X-ray diffraction data give evidence for an increase in the a lattice parameter with increasing PbO content and partial occupancy of Pb in the Ta sites leading to the formula Pb1.5+x2+(Ta2−yPby4+)O7−δ (0.0 < x < 0.5; 0.0 < y < 0.6) for this phase. It has also been found that the intermediate members of the solid solutions are metastable and tend to segregate into Pb-deficient and Pb-excess compositions leading to significant compositional inhomogeneity for the intermediate members.

Low‐Temperature Synthesis of Lead Tantalate Pyrochlore Solid Solutions Pb1.5+x(Ta2−yPby)O7−δ (0.0 < x < 0.5; 0.0 < y < 0.6)

Formation of lead niobate pyrochlores by the reaction of PbO with Nb2O5 in various molar ratios and at various temperatures has been investigated. It has been shown that for a PbO/Nb2O5 molar ratio between 1.5 and 3.0, a pyrochlore solid solution having cubic symmetry is formed at low temperatures (∼500-600°C). X-ray diffraction data show evidence for the existence of compositional inhomogeneity for this phase which contains part of the Pb in the Nb site leading to the formula Pb1.5+x(Nb2-yPby)O7-delta (0.0 < x < 0.5; 0.0 < y < 0.5). A phase-pure Pb-deficient pyrochlore (Pb1.5Nb2O6.5) and Pb-excess pyrochlores (Pb2.5Nb2-O8, Pb3Nb2O8) are formed by the decomposition of this cubic solid solution and subsequent reaction at high temperatures. These results indicate that the mechanism of the structural transformation from the low-temperature (LT) cubic solid solution to the corresponding high-temperature (HT) phases is reconstructive.

Krishnan Sreedhar

Papers

Formation of Lead Magnesium Niobate Perovskite from Niobate Precursors Having Varying Magnesium Content

Low‐Temperature Synthesis of Lead Tantalate Pyrochlore Solid Solutions Pb1.5+x(Ta2−yPby)O7−δ (0.0 < x < 0.5; 0.0 < y < 0.6)

Formation and Transformation of Cubic Lead Niobate Pyrochlore Solid Solutions

Evidence for size effect on insulator-metal transition in C: (H; S)

Foxtail millet husk as an innovative biomass in the preparation of silica-silver composite with antimicrobial and free radicle scavenging activities