Composites containing pure, uniform, and well-dispersed ferroelectric barium titanate (BaTiO3) nanocrystallites with various particle sizes as active phase and polyvinylidene fluoride (PVDF) polymer as matrix are fabricated using a two-step mixing and hot-pressing technique. The dependences of the dielectric and ferroelectric properties of the as-prepared composites on the nanoparticle sizes are investigated systematically. The polarization-electric field hysteresis loops are displayed, indicating the ferroelectricity for the BaTiO3/PVDF nanocomposites. The remanent polarization is found to increase as the size of BaTiO3 particles increases from 25 to 500 nm. The dielectric constant of the composites exhibits a complex variation as a function of the BaTiO3 nanoparticle sizes: it reaches a maximum value in the composites with BaTiO3 nanoparticle sizes of 80-100 nm and decreases again when the particle size is further reduced under 50 nm. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3443582]Natural Science and Engineering Research Council of Canada (NSERC) [203773]; National Natural Science Foundation of China [20725310, 20673085]; National Basic Research Program of China [2007CB815303

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Single crystals of lead chromium phosphate Pb 3 Cr 2 (PO 4 ) 4 were grown by a flux technique and characterized by X-ray powder and single crystal diffraction, differential thermal analysis, polarized light microscopy and magnetic measurements. Two polymorphic structures have been identified: a monoclinic Pb 3 Cr 2 (PO 4 ) 4 of space group P2 1 /c ( 14) and a tetragonal Pb 3 Cr 2 (PO 4 ) 4 of space group P4 1 2 1 2 (94), and their phase correlation is described. Both structures consist of a three-dimensional framework which is composed of PO 4 tetrahedra and CrO 6 octahedra connected via vertices. Lead ions are situated at the cavities of the framework, but the positions of lead ions in the monoclinic Pb 3 Cr 2 (PO 4 ) 4 are different from those in the tetragonal Pb 3 Cr 2 (PO 4 ) 4 . The Pb 3 Cr 2 (PO 4 ) 4 crystals are found to exhibit interesting physical properties. The ferroelastic domain structures reveal characteristic patterns of the tetragonal and the monoclinic symmetry of the crystals. The birefringence of the tetragonal crystals decreases with increasing temperature. The monoclinic crystal is found to undergo a series of magnetic phase transitions upon cooling, from a paramagnetic phase (from room temperature down), to an antiferromagnetic phase below T N ¼ 6 K, and then to a weakly ferromagnetic phase below the Curie temperature T C ¼ 4 K, with a magnetic hysteresis loop displayed at 2 K.

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Lead I 4900 Synthesis and Crystal Structural Characterization of a New Lead Oxide Chromate Phosphate: Pb 5 O(CrO 4 )(PO 4 ) 2 . -Orange single crystals of the new title compound are prepared by a self-flux technique from a mixture of PbO, CrO2, NH4H2PO4, and H3BO3 powders (Pt crucible1170°C, 24 h). The compound crystallizes in the orthorhombic space group Pcmn with Z = 4. The crystal structure contains strictly alternating CrO4 and PO4 tetrahedra linking four crystallographically different Pb atoms with Pb coordination numbers range from four to seven atoms. The multiple crystallographic sites and the rich coordination environment of Pb in a single compound appear to be unusual. -(MAO*, S.-Y.; MAO, Y.-P.; ZHONG, M.-P.; YE, Z.-G.;