Bi2-xPbxSr2CaCu2O8+d solid solutions with substitution of Sr or Ca by Y, Nd or La were fabricated at 760 - 79°C in N2-flow. The as-synthesized solutions were oxidized in air under isothermal condition and tested with XRD, TGA chemical analysis, TEM, XANES. Effect of rare-earth element content on oxidation kinetics and microstructure of the product is discussed.

In this article we present the main features and structural relationships between thortveitite-type and thortveitite-like germanates compounds. We describe in detail the crystal structures, how they are built and the difference between them. Bond-valence and polyhedra distortion analysis are made and crystal structure stability ranges are given.

A carbothermal reaction process was employed to synthesize nano-sized boron carbide particles. The reactions were carried out by heating a mixture of boric oxide powder and amorphous carbon reactant under a flow of argon atmosphere in a conventional high temperature tube furnace at 1350–1700 °C for 1–4 h. In order to obtain stoichiometric powder product, additional pure boron powder was added to the reaction mixture to compensate for the boron loss in the form of B2O2/B2O3 vapor during the reaction. The effect of the structure and morphology of the precursor materials on that of the products was also investigated. X-ray diffraction (XRD) studies indicated that the powdered product prepared under optimized reaction conditions was crystalline boron carbide. Transmission electron microscopy (TEM) observations showed that the product nanoparticles ranged from 50 nm to 250 nm with the average size between 100 nm and 150 nm depending on the reaction conditions. Some boron carbide particles were as small as 50 nm. Energy dispersive spectroscopy (EDS) was also used to determine the stoichiometry of the boron carbide nanoparticle products.

The coercive field measured from ferroelectric hysteresis loop for pure and Mg:SLT (0.5 mol% doped) crystals were found to be independent of ramp rate of voltage, while it depends strongly on ramp rate for Mg:SLT (1 mol% doped) crystals. The measured coercive field decreased monotonously depending on the Mg concentration and low Ec value of 6 kV/cm is obtained for Mg(1.0 mol%)SLT crystal. Internal field of about 1 kV/cm present in pure SLT completely gets vanished in Mg(1.0 mol%)SLT. Spontaneous polarization is insensitive to the Mg addition. The origin of the internal field and large changes in switching fields appear largely to be dependent on the [Li]/[Li+Ta] ratio in crystals. On repeated cycling, the coercive field is found to have a marginal variation in pure and Mg doped SLT crystals.

Textured bismuth titanate (Bi4Ti3O12), the simplest and best known compound among the bismuth layer-structure ferroelectrics is interesting because of its peculiar switching behavior which results from a small c-axis component of the spontaneous polarization and a small coercive force. We prepared Bi4Ti3O12 ceramics through the templated grain growth (TGG) method combined with the spark plasma sintering (SPS) method. The TGG method was developed to provide a simpler way of creating textured ceramic microstructures. The SPS method enables a compact powder to be sintered under uniform heating to a high density at relative low temperatures and with much shorter sintering periods than with conventional sintering.

We obtained a Bi4Ti3O12 precursor powder through a co-precipitation method with Ti alkoxide and Bi oxide as raw materials. Platelet Bi4Ti3O12 was synthesized from the precursor powder through a flux method using NaCl and KCl. The obtained platelet Bi4Ti3O12 had a high aspect ratio. The ceramics were prepared by SPS treatment using a mixture of the platelet Bi4Ti3O12 and the amorphous precursor powder. As a result, dense ceramics could be easily obtained without crystalline amorphous precursors and grain growth was not observed during the sintering. After heat treatment of the ceramics, we obtained highly textured, high density Bi4Ti3O12 ceramics. The ceramics showed high orientation, above 70%, for the c-axis direction and high density of over 85%.

Ternary rare-earth transition-metal antimonides RExMy Sbz have provided fertile ground for discovering materials with varied electrical and magnetic properties such as superconductivity and ferromagnetism. The properties of two important classes of these compounds, RE 3TiSb5 and RECrSb3, have been previously investigated. These studies have now been extended to RE 3 MSb5 (M = Zr, Hf), which show anomalies in their resistivity curves suggestive of electronic transitions, and YbCrSb3, which undergoes long-range magnetic ordering at 285 K, the highest T c observed so far of all RECrSb3 members. Strong magnetic exchange interactions develop through coupling of f and d electrons in these compounds. The substitution of uranium for rare earth in RE 3 MSb5 results in the compounds U3 MSb5 (M = Zr, Hf, Nb), which also display prominent transitions in their electrical resistivity and magnetic susceptibility curves.

Processing of nanoreactant energetic system, Al-TiO2, in the thermal explosion mode of combustion synthesis was investigated. Simultaneous combustion synthesis and densification experiments were carried out in a uniaxial press to obtain homogeneous as well as functionally graded products of the above reactant system. It was demonstrated that TiAl3-Al2O3 composite product synthesized from Al-TiO2 reactant system retained its sub-microstructure despite a short term exposure to higher temperatures. Composite materials with densities of 96–98% of the theoretical densities were obtained. The effect of several key processing parameters such as initial composition of reactants and temperature-pressure conditions on morphology of combustion synthesized product, their phase composition, and residual porosity were investigated. DSC, XRD, SEM, and LIBS analyses were used to characterize both reactants and products.

The Sr1-x Prx Bi2Ta2O9 (SBT-Pr) ferroelectric ceramic doped with Praseodymium in the range of concentration between 0 and 0.20 was studied. X-ray diffraction patterns show that the Pr-ion substitutes the Sr-ion in the main structure (A21 am space group) and, as a consequence of this substitution the unit cell decreases monotonically. Thermoelectric Analysis (ε vs T) and ferroelectric hysteresis measurements were performed. From the ε-T curves it was observed that the transition temperature depends almost linearly on Pr content. Broad phase transitions were also observed, a typical behavior of ferroelectric materials with diffuse phase transition (DPT). An increase in the diffuseness coefficient is obtained by increasing Pr content according to the Isupov model, due to the higher cationic disorder in the structure, resulting in the loss of the long-range ferroelectric ordering. The hysteresis loop indicates that the substitution of Sr2+ by Pr3+,4+ lowers the polarization due possible to strong pinning domain mechanisms that obstruct long range ferroelectric ordering.

High purity alumina is usually prepared using various intermediate aluminium compounds such as aluminium nitrate, aluminium alkoxides etc., as precursors. In fact the above mentioned intermediate aluminium compounds themselves are produced from aluminium metal. The present investigation is concerned with examining the feasibility of using aluminium hydroxides prepared by hydrolyzing aluminium metal, for sol gel processing. The study assumes added significance in view of the claims of Alcoa that it is possible to produce high purity aluminium metal in large quantities economically.

During the present investigation sols were prepared by using various hydroxides, ie., bayerite, gibbsite and boehmite. Sol gel transition was observed only in the case of boehmite sol and this was gelated by either forced gelation method to prepare powder or controlled gelation method to prepare monoliths.

Transparent Xerogels (boehmite) could be prepared by controlled gelation method but the presence of a thin layer of bayerite often resulted in translucency. Crack free monoliths could be prepared by heating the xerogels at a low heating rate(< 1 °C/min). It was found that sol gel processed boehmite transformed to alpha alumina at a relatively lower temperature (∼ 1080 °C ) than the as prepared boehmite which transformed at about 1200 °C.

We present the more relevant results of various cationic substitutions in the RuSr 2 GdCu 2 O 8 (Ru-1:2:1:2 ) compound. The substitutions were synthesized by solid-state reaction at ambient pressure in the following systems: Ru 1−x Sr 2 GdCu 2+x O 8 (0.0 < x < 1.0), Ru(Sr 2-x Ca x )GdCu 2 O 8 (0 < x < 2.0) and RuSr 2(Gd1-x Ln x )Cu 2 O 8 (0 < x < 0.9) with Ln = Dy, Ho, Er, Yb and Lu. All of them were isostructural to Ru-1:2:1:2 compound with tetragonal unit cells. The phases have been characterized by X-Ray powder Diffraction (XRD), observing a solid solution (ss ) up to x = 0.4 for Ru ions replaced by Cu ions, x = 0.1 when we substitute Sr atoms by Ca atoms, and x = 0.7 changing Gd ions by Ln ions. As a result of the Scanning Electron Microscopy (SEM), the grain sizes were discovered to be 1 – 10 μm. The Energy Dispersive X-ray spectroscopy (EDX) analysis permitted us to analyze the impurities that we did not detect with XRD. We observed semiconducting, isolated and ferromagnetic behaviors. No superconducting transition could be observed for these ambient preparation conditions.

The discovery of the new superconductor MgB2 with critical temperature of Tc = 39 K stimulated great activity in search for materials with higher Tc. Theoretical works predicted the possibility of obtaining such superconducting materials in other borides also, in particular in AgB2. It was predicted in these works that diborides of metals having the AlB2 type structure, among them AgB2 may have superconductivity with a Tc higher than 39 K. In an early very short report the lattice parameters of AgB2 were evaluated in a synthesized specimen. However, no other indication exists that AgB2 was ever produced. We report the preliminary results of our attempts to prepare AgB2 films.

Thin films of Ag-B were produced by magnetron cosputtering in Ar ambient from two separate targets that of B and Ag on Si (100) substrates. The specimens were subjected to X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photo spectroscopy (XPS), Auger analysis and optical microscope (OM) investigations. Resistivity measurements in a wide temperature range were measured. No superconductivity was yet observed in the range ∼10 – 200. K on the basis of resistivity measurements. Preliminary results indicate that AgB2 might be an unstable phase.

The features of the structure of nanorystalline Ce1-xPrxO2-y system (0 ≤ × ≤ 0.5) prepared via a complex polymerized precursor (Pechini) route have been elucidated by using a combination of spectroscopic (XANES, XPS) and structural (TEM, neutron diffraction) methods. Within the studied range of composition, the structure of all samples air annealed at 500 °C corresponds to single-phase fluorite-like solid solution. The relative content of Pr3+ both in the bulk and in the surface layer appears to be as high as 20–50%. The Rietveld refinement revealed non-monotonous variation of structural parameters (lattice parameter, domain size, microstrain density, Ce-O and O-O distances) and residual lattice hydroxyls concentration with Pr content. Clustering of defects along with variation of the mean Pr cation radius/charge state and disordering of the surface layer/ domain boundaries appear to be responsible for the observed features.

There is an increasing interest in sol-gel synthesis of nitrides. The ability to deposit films of these materials by dip- or spin-coating will increase the range of applications in which they are viable and is an important step toward general sol-gel processing of nitride materials.

With transition metals, the ammono based analogue of the well established alkoxy route to gels is inherently difficult to control. Due to the basicity of the system, the overwhelming tendency is of the starting materials to favour particle growth which results in a precipitate rather than a stable emulsion, unless both environment and synthetic pathway are carefully controlled. Hence reports to date of sol-gel routes to nitrides describe production of powders. We report work on a sol-gel route to titanium nitride with the ammonolysis of titanium amides controlled by temperature and chemical moderators, resulting in stable emulsions useful for dip-coating.

A new member of the LnMIn5 family, ErCoIn5, has been synthesized by a flux-growth method. The structure of ErCoIn5 was determined by single crystal X-ray diffraction. It crystallizes in the tetragonal space group P4/mmm, Z = 1, with lattice parameters a = 4.5400(4) and c = 7.3970(7) Å, and V = 152.46(2) Å3. Electrical resistivity data show metallic behavior. Magnetic susceptibility measurements show this compound to be antiferromagnetic with TN = 5.1 K. We compare these experimental results with those of LaCoIn5 in an effort to better understand the effect of the structural trends observed on the transport and magnetic properties.

As part of an ongoing program exploring the solvothermal synthesis and crystal chemistry of organically templated metal fluorides, a novel compound [C2N2H10]0.5[Y2F7] has been isolated. The structure consists of a continuous 3-D array of YF8 and YF9 polyhedra linked through corners, edges and faces to enclose small channels in which the template cations sit. The structure is stable up to 400°C, at which point template loss causes structural collapse. This structure represents the first yttrium or rare-earth fluoride templated by organic cations, and suggests a wide variety of novel structure types will be amenable via such routes, possibly leading to novel families of luminescent materials.

A new series of triple layered Ruddlesden-Popper compounds of the general formula (LixVO)La2Ti3O10, where X = 0.83, 0.93, 1.4 and 1.8, have been prepared. Lithium is intercalated into the layered perovskite in a reductive manner to produce new mixed valence compounds. The structure of the parent, (VO)La2Ti3O10, is maintained upon intercalation. Above a certain lithium content, the magnetic behavior of (LixVO)La2Ti3O10 changes from paramagnetic, for X = 0.83, 0.93, 1.4, to a magnetically ordered material for (Li1.8VO)La2Ti3O10.

The synthesis of non-linear optical (NLO) materials that are transparent into the deep-UV (<200 nm) region is an important component in the development of advanced optical technology. Such materials are sought after for their potential applications in the fields of high resolution photolithography, micro-machining, and laser spectroscopy. Borates are one class of solid-state materials that have received consideration for these applications because of their favorable physical and optical properties. One such compound, Sr2Be2B2O7 (SBBO) has been reported to be transparent below 200 nm, and exhibits a large second harmonic generation (SHG) coefficient. Significant difficulties in the flux growth of large, high quality crystals have prevented this material from further development. We have successfully grown large crystals of SBBO by a hydrothermal synthetic method for the first time, and have characterized their physical properties. The synthesis and structure of a new material encountered during the synthesis of SBBO, LiBeSr2B3O8, is also reported here.

Ferroelectricity was induced in SrTiO3 by the Sr exchange for Pr ion in the A site of the perovskite ABO3-type structure. X-ray diffraction patterns show single phase crystalline structure in the SrxPr1-xTiO3 compound for x=0, 0.025, 0.050, 0.075 and 0.1 compositions. Rietveld refinement shows that the unit cell volume decreases with the increasing of Pr content as a consequence of the difference between Sr/Pr ionic radii. Furthermore, high-temperature differential thermoanalysis (DTA) displays a small anomaly at about 118 °C which is probably due to the Pr ion producing a distortion of the perovskite structure via an off-center site. This deformation in the lattice induces a measurable polar behavior of the solid solution. Dielectric permittivity (ε vs T) measurements display a well defined peak at about 238 °C. Furthermore, a well defined hysteresis loop at 30 °C with a remnant polarization that tends to decrease with increasing Pr concentration is observed. Both experimental results confirm the ferroelectric state induced by the Pr ion.

The thermodynamic stability of the three nearly energy degenerate crystal structures of PtO2 is studied here with first-principles-based calculations of their free energies. For P = 0 the α-(CdI2) structure is the thermodynamically stable phase at low temperature, while the β-(CaCl2) structure is stable at high pressure. The β'-(rutile) structure represents an unstable fixed point on the potential energy surface, or is possibly just barely bound. These results reconcile seemingly contradictory findings and answer longstanding questions about PtO2.

Chemical processing of inorganic materials demands an understanding of the precursor chemistry at the molecular level. Although chemical compounds imitating atomic composition or bonding features of solid phases are efficient templates for a controlled evolution of nano-matter, the intrinsic advantages of this approach, such as atomic level mixing of the constituents and phase-selective synthesis, rely on the chemistry involved in the transformation of molecules to materials. Therefore, a better understanding of principles underlying chemical processing is necessary to enable a rational synthesis of materials. We have deposited MgAl2O4 thin films by the chemical vapor deposition of two Mg-Al alkoxide precursors, [MgAl2(OPri)8] and [MgAl2(OBut)8], which reveal that precursor attributes such as vapor pressure and ligand elimination mechanisms influence the microstructure and material properties of the spinel films. Under similar growth conditions, [MgAl2(OPri)8] produces rough and poorly crystalline spinel films, whereas crystalline deposits and dense microstructure were obtained in the case of [MgAl2(OBut)8]. The films were characterized by XRD, SEM, TEM, XPS and nano-indentation studies.