A facile urea-assisted hydrothermal synthesis and systematic characterization of hydroxyapatite (HA) with calcium nitrate tetrahydrate and diammonium hydrogen phosphate as precursors are reported. The advantage of the proposed technique over previously reported synthetic approaches is the simple but precise control of the HA crystals morphology, which is achieved by employing an intensive, stepwise, and slow thermal decomposition of urea as well as varying initial concentrations of starting reagents. Whereas the plate-, hexagonal prism- and needle-like HA particles preferentially growth along the c-axis, the smaller and fine-plate-like HA crystals demonstrate crystal growth along the (102) and (211) directions, uncommon for HA. Furthermore, it was established that the hydrothermally derived powdered products are phase-pure HA containing CO3 2− anions in the crystal lattice, that is, AB-type carbonated hydroxyapatite. Transmission electron microscopy (TEM) and electron diffraction (ED) of selected samples reveal that the as-prepared HA crystals are single-crystalline and exhibit a nearly defect-free microstructure. The hardness and elastic modulus of the hexagonal prism-like HA crystals have been investigated on a nanoscale using the nanoindentation technique; the observed trends are discussed.

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In this report, we describe a novel solvothermal procedure for the synthesis of nanosized particles of barium titanate (BaTiO 3 ). We have been able to synthesize large amounts of nearly uniform sized BaTiO 3 nanocrystals in the size range of 5-37 nm. The advantages of our technique over other previously reported hydrothermal/ solvothermal approaches are the high yield and the simple but precise control of the size of the particles, which is very conveniently achieved by changing the water content of the reaction mixture in a measured way. The particles are systematically characterized by powder X-ray diffraction (XRD), Raman scattering, scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron diffraction (ED), high-resolution TEM (HRTEM), disc centrifugation, thermogravimetric and differential thermal analyses (TGA-DTA), infrared spectroscopy (IR), and inductively coupled plasma-optical emission spectrometer (ICP-OES). The as-synthesized BaTiO 3 nanopowders contain BaCO 3 byproduct as well as internal OHgroups and residual solvent species that can be removed by acid washing following heating. However, it is shown that this procedure results in the substantial change of the chemical composition and strong degradation of real microstructure of nanosized BaTiO 3 particles.

A series of biocomposite materials was successfully prepared by reinforcing advanced calcium phosphate cement with hydroxyapatite fibrous and elongated plate-like particles. Powder X-ray diffraction showed that ball-milled biocomposite precursors (dicalcium and tetracalcium phosphates) entirely transform to a single phase hydroxyapatite end product within 7 h at 37 °C. Electron microscopy showed that the resultant biocomposites are constituted of nanoscaled cement particles intimately associated with the reinforcement crystals. The influence of shape, size, and concentration of the hydroxyapatite filler on the compression strength of reinforced cements is discussed. The best compression strength of 37 ± 3 MPa (enhancement of ∼50% compared to pure cement) was achieved using submicrometer-sized hydroxyapatite crystals with complementary shapes. Nanoindentation revealed that averaged elastic modulus and hardness values of the cements are consistent with those reported for trabecular and cortical human bones, indicating a good match of the micromechanical properties for their potential use for bone repair. The stiffness of the biocomposites was confirmed to gradate-compliant cement matrix, cement-filler interface, and stiff filler-as a result of the structuring at the nanometer-micrometer level. This architecture is critical in conditioning the final mechanical properties of the functional composite biomaterial. In vitro cell culture experiments showed that the developed biomaterial system is noncytotoxic.

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Structure D 2000Sn4As3 Revisited: Solvothermal Synthesis and Crystal and Electronic Structure.-The title compound is solvothermally prepared from a mixture of the elements, en, and NH4Cl (autoclave, 473-513 K, 20-120 h), and its crystal structure is re-determined by single crystal XRD. Sn4As3 crystallizes in the trigonal noncentrosymmetric space group R3m with Z = 3. The structure consists of alternating layers of As and Sn atoms which are combined into seven-layer blocks with short Sn-Sn distances of 3.24 Å between adjacent blocks. TB-LMTO-ASA band structure calculations indicate metallic behavior of Sn4As3. The compound is further characterized by 119 Sn Moessbauer spectroscopy. -(KOVNIR*, K.; KOLEN'KO, Y. V.; BARANOV, A. I.; NEIRA, I. S.; SOBOLEV, A. V.; YOSHIMURA, M.; PRESNIAKOV, I. A.; SHEVELKOV, A. V.; J. Solid State Chem. 182 (2009) 3, 630-639; Dep. Mater. Sci., Lomonosov Moscow State Univ., Moscow 119992, Russia; Eng.) -W. Pewestorf 25-005