Structural and spectroscopic properties of pure and doped Ba6Ti2Nb8O30 tungsten bronze.

Pure and doped Ba(6)Ti(2)Nb(8)O(30) (BTN), obtained by substituting M = Cr, Mn, or Fe on the Ti site (Ba(6)Ti(2-x) M(x)Nb(8)O(30), x = 0.06 and 0.18) and Y and Fe on the Ba and Ti sites, respectively (Ba(6-x)Y(x)Ti(2-x)Fe(x)Nb(8)O(30), x= 0.18), are synthesized. The influence of cation doping on the local structure, the cation oxidation state, and the possible defect formation able to maintain the charge neutrality are investigated by spectroscopic (electron paramagnetic resonance (EPR) and micro-Raman), structural (X-ray powder diffraction) and transport (impedance spectroscopy, thermoelectric power) measurements, in the temperature range of 300-1200 K in air and N(2) flow. Starting from the valence state of the doping ions (Fe(3+), Cr(3+), and Mn(2+)), determined by EPR, and from thermoelectric power measurements, evidencing a negative charge transport, different charge-compensating defect equilibria, based on the creation of positive electron holes or oxygen vacancies and electrons, are discussed to interpret the conductivity results.

Cation distribution in LiMgVO4 and LiZnVO4: structural and spectroscopic study.

The room temperature cation occupancy in LiMgVO(4) and LiZnVO(4) crystallographic sites is obtained by means of the combined use of X-ray powder diffraction (XRPD), (7)Li and (51)V magic angle spinning nuclear magnetic resonance (MAS NMR), and micro-Raman measurements. In the LiMgVO(4) Cmcm orthorhombic structure, the 4c (C(2)(v) symmetry) tetrahedral vanadium site is fully ordered; on the contrary, the Li 4c tetrahedral site and the 4b (C(2)(h) symmetry) Mg octahedral site display about 22% of reciprocal cationic exchange. Higher cationic disorder is observed in LiZnVO(4): the three cations can distribute on the three tetrahedral and distinct sites of the R-3 structure. XRPD and MAS NMR analysis results highly agree for what concerns vanadium ion distribution on the three cationic sites (about 25, 26, and 47%). From the full profile fitting of XRPD patterns with the Rietveld method, it is also obtained that Li(+) displays a slightly preferred occupation of the T1 position (approximately 55%) and Zn(2+) of the T2 position (approximately 46%). The vibrational spectra of the two compounds are characterized by different peak positions and broadening of the Raman modes, reflecting the cation distribution and the local vibrational unit distortion. A comparison is also made with recent Raman results on Li(3)VO(4). High temperature XRPD measurements rule out possible structural transitions up to 673 K for both compounds.

Transport and structural properties of pure and Cr doped Li3VO4.

This study deals with the effects of 5 and 10% chromium additions on the transport and structural properties of Li3VO4. The Cr substitution is easily obtained without impurity phases and does not affect the room- and high-temperature host crystal structure, as evidenced by X-ray powder diffraction and micro-Raman analysis. The EPR signals are interpreted in terms of quantified amounts of Cr ions in 5+ and 3+ valence states. Suitable 7Li and 51V MAS NMR spectra simulations agree with the EPR results about the relative amount of Cr5+ and Cr3+ ions substituted in V5+ and Li+ sites, respectively. The Cr3+ presence on Li site, also suggested by Raman results and Rietveld refinements, requires Li vacancies to maintain the charge neutrality. The p-type conductivity, suggested by the positive thermoelectric power coefficients, significantly increases by the cation doping up to an order of magnitude.

Polymorphism of rac-5,6-diisobutyryloxy-2-methylamino-1,2,3,4-tetrahydro-naphthalene hydrochloride (CHF 1035). I. Thermal, spectroscopic, and X-ray diffraction properties.

The polymorphism of rac-5,6-diisobutyryloxy-2-methylamino-1,2,3,4-tetrahydro-naphthalene hydrochloride (CHF 1035) was investigated. Three different crystal forms (Form I, Form II, and Form III) were obtained by recrystallization procedures from common organic solvents. The polymorphs were characterized by Raman and carbon-13 nuclear magnetic resonance ((13)C NMR) spectroscopy, in solution and in solid state (cross polarization-magic angle spinning), powder X-ray diffractometry, and thermal methods (differential scanning calorimetry, hot stage microscopy, and thermogravimetry). Moreover, the diffraction patterns of Form I, collected at controlled temperatures, gave evidence of the presence of two reversible structural rearrangements at approximately 60 and approximately 75 degrees C. These structural variations were confirmed by the results obtained by differential scanning calorimetry and hot stage microscopy techniques. The analysis of the Raman spectra allowed the identification of peculiar absorption bands for each polymorph. Form III was the stable crystal form at room temperature as determined by the basis of slurry conversion method.