Improved Li storage performance of SnO nanodisc on SnO2quantum dots embedded carbon matrix.

Li-ion batteries with conversion type anode are attractive choice, for electric vehicles and portable electronic devices, because of their high theoretical capacity and cycle stability. On the contrary, enormous volume change during lithiation/delithiation and irreversible conversion reaction limits use of such anodes. To overcome these challenges, incorporating nano-sized SnOxon flexible carbonaceous matrix is an efficient approach. A facile and scalable fabrication of SnO nanodisc decorated on SnO2quantum dots embedded carbon (SnOx@C) is reported in the present study. Detailed structural and morphological investigation confirms the successful synthesis of SnOx@C composite with 72.3 wt% SnOxloading. The CV profiles of the nanocomposite reveal a partial reversibility of conversion reaction for the active materials SnOx. Such partial reversible conversion enhances the overall capacity of the nanocomposite. It delivers a very high discharge capacity of 993 mAh g-1at current density of 0.05 A g-1after 200 cycles; which is 2.6 times higher than that of commercial graphitic anode (372 mAh g-1) and very close to the calculated capacity of the SnOx@C composite. This unique nanocomposite remarkably improves Li storage performance in terms of reversible capacity, rate capability and cycling performance. It is established that such engineered anode can efficiently reduce the electrode pulverization and in turn make conversion reaction of tin partially reversible.

Pressure and Temperature Dependent Structural Studies on Hollandite Type Ferrotitanate and Crystal Structure of a High Pressure Phase.

The structural stability and phase transition behavior of tetragonal (I4/m) hollandite type K2Fe2Ti6O16 have been investigated by in situ high pressure X-ray diffraction using synchrotron radiation and a diamond anvil cell as well as by variable temperature powder neutron and X-ray diffraction. The tetragonal phase is found to be stable in a wider range of temperatures, while it reversibly transforms to a monoclinic (I2/m) structure at a moderate pressure, viz. 3.6 GPa. The pressure induced phase transition occurs with only a marginal change in structural arrangements. The unit cell parameters of ambient (t) and high pressure (m) phases can be related as am ∼ at, bm ∼ ct, and cm ∼ bt. The pressure evolution of the unit cell parameters indicates anisotropic compression with ßa = ßb ≥ ßc in the tetragonal phase and becomes more anisotropic with ßa ≪ ßb < ßc in the monoclinic phase. The pressure-volume equations of state of both phases have been obtained by second order Birch-Murnaghan equations of state, and the bulk moduli are 122 and 127 GPa for tetragonal and monoclinic phases, respectively. The temperature dependent unit cell parameters show nearly isotropic expansion, with marginally higher expansion along the c-axis compared to the a- and b-axes. The tetragonal to monoclinic phase transition occurs with a reduction of unit cell volume of about 1.1% while the reduction of unit cell volume up to 6 K is only about 0.6%. The fitting of temperature dependent unit cell volume by using the Einstein model of phonons indicates the Einstein temperature is about 266(18) K.

High Pressure Phases and Amorphization of a Negative Thermal Expansion Compound TaVO5.

Negative thermal expansion material TaVO5 is recently reported to have pressure induced structural phase transition and irreversible amorphization at 0.2 and above 8 GPa, respectively. Here, we have investigated the high pressure phase of TaVO5 using in situ neutron diffraction studies. The first high pressure phase is identified to be monoclinic P21/ c phase, same as the low temperature phase of TaVO5. On heating, amorphous TaVO5 transformed to a new crystalline phase, which showed signatures of higher coordination of vanadium indicating pressure induced amorphization (PIA). PIA observed in TaVO5 might be due to the kinetic hindrance of pressure induced decomposition (PID) into a compound with higher coordination of vanadium. Mechanism of PIA observed in TaVO5 is investigated by carrying out ex situ Raman, XRD, XPS, and XAS measurements. We have also proposed a pressure-temperature phase diagram of TaVO5 qualitatively delineating the phase boundaries between the ambient orthorhombic, monoclinic, and amorphous phases.

Stability of FeVO4 under Pressure: An X-ray Diffraction and First-Principles Study.

The high-pressure behavior of the crystalline structure FeVO4 has been studied by means of X-ray diffraction using a diamond-anvil cell and first-principles calculations. The experiments were carried out up to a pressure of 12.3 GPa, until now the highest pressure reached to study an FeVO4 compound. High-pressure X-ray diffraction measurements show that the triclinic P1̅ (FeVO4-I) phase remains stable up to ≈3 GPa; then a first-order phase transition to a new monoclinic polymorph of FeVO4 (FeVO4-II') with space group C2/ m is observed, having an α-MnMoO4-type structure. A second first-order phase transition is observed around 5 GPa toward the monoclinic ( P2/ c) wolframite-type FeVO4-IV structure, which is stable up to 12.3 GPa in coexistence with FeVO4-II'. The unit cell volume reductions for the first and second phase transitions are Δ V = -8.5% and -13.1%. It was observed that phase transitions are irreversible and both high-pressure phases remain stable once the pressure is released. Calculations were performed at the level of the generalized gradient approximation plus Hubbard correction (GGA+ U) and with the hybrid Heyd-Scuseria-Ernzerhof (HSE06) exchange-correlation functional in order to have a good representation of the pressure behavior of FeVO4. We found that theoretical results follow the pressure evolution of structural parameters of FeVO4, in good agreement with the experimental results. Also, we analyze FeVO4-II (orthorhombic Cmcm, CrVO4-type structure) and -III (orthorhombic Pbcn, α-PbO2-type structure) phases and compare our results with the literature. Going beyond the experimental results, we study some possible post-wolframite phases reported for other compounds and we found a phase transition for FeVO4-IV to raspite (monoclinic P21/ c) type structure (FeVO4-V) at 36 GPa (Δ V = -8.1%) and a further phase transition to the AgMnO4-type (monoclinic P21/ c) structure (FeVO4-VI) at 66.5 GPa (Δ V = -3.7%), similar to the phase transition sequence reported for InVO4.

Phase Transformation, Vibrational and Electronic Properties of K2Ce(PO4)2: A Combined Experimental and Theoretical Study.

Herein we report the high-temperature crystal chemistry of K2Ce(PO4)2 as observed from a joint in situ variable-temperature X-ray diffraction (XRD) and Raman spectroscopy as well as ab initio density functional theory (DFT) calculations. These studies revealed that the ambient-temperature monoclinic (P21/n) phase reversibly transforms to a tetragonal (I41/amd) structure at higher temperature. Also, from the experimental and theoretical calculations, a possible existence of an orthorhombic (Imma) structure with almost zero orthorhombicity is predicted which is closely related to tetragonal K2Ce(PO4)2. The high-temperature tetragonal phase reverts back to ambient monoclinic phase at much lower temperature in the cooling cycle compared to that observed at the heating cycle. XRD studies revealed the transition is accompanied by volume expansion of about 14.4%. The lower packing density of the high-temperature phase is reflected in its significantly lower thermal expansion coefficient (αV = 3.83 × 10-6 K-1) compared to that in ambient monoclinic phase (αV = 41.30 × 10-6 K-1). The coexistences of low- and high-temperature phases, large volume discontinuity in transition, and large hysteresis of transition temperature in heating and cooling cycles, as well as drastically different structural arrangement are in accordance with the first-order reconstructive nature of the transition. Temperature-dependent Raman spectra indicate significant changes around 783 K attributable to the phase transition. In situ low-temperature XRD, neutron diffraction, and Raman spectroscopic studies revealed no structural transition below ambient temperature. Raman mode frequencies, temperature coefficients, and reduced temperature coefficients for both monoclinic and tetragonal phases of K2Ce(PO4)2 have been obtained. Several lattice and external modes of rigid PO4 units are found to be strongly anharmonic. The observed phase transition and structures as well as vibrational properties of both ambient- and high-temperature phases were complimented by DFT calculations. The optical absorption studies on monoclinic phase indicated a band gap of about 2.46 eV. The electronic structure calculations on ambient-temperature monoclinic and high-temperature phases were also carried out.

Temperature dependent structural, vibrational and magnetic properties of K3Gd5(PO4)6.

Herein we report the evolution of the crystal structure of K3Gd5(PO4)6 in the temperature range from 20 K to 1073 K, as observed from variable temperature X-ray diffraction and Raman spectroscopic studies. K3Gd5(PO4)6 has an open tunnel containing a three dimensional structure built by [Gd5(PO4)6]3- ions which in turn are formed of PO4 tetrahedra and GdOn (n = 8 and 9) polyhedra. The empty tunnels in the structure are occupied by K+ ions and maintain charge neutrality in the lattice. Evolution of unit cell parameters with temperature shows a systematic increase with temperature. The average axial thermal expansion coefficients between 20 K and 1073 K are: αa = 10.6 × 10-6 K-1, αb = 5.5 × 10-6 K-1 and αc = 16.4 × 10-6 K-1. The evolution of distortion indices of the various coordination polyhedra with temperature indicates a gradual decrease with increasing temperature, while those of Gd2O9 and K2O8 polyhedra show opposite trends. The overall anisotropy of the lattice thermal expansion is found to be controlled largely by the effect of temperature on GdOn polyhedra and their linkages. Temperature dependent Raman spectroscopic studies indicated that the intensities and wavenumbers of most of the Raman modes decrease continuously with increasing temperature. Anharmonic analyses of Raman modes indicated that the lattice, rigid translation and librational modes have larger contributions towards thermal expansion of K3Gd5(PO4)6 compared to high frequency internal modes. The temperature and field dependent magnetic measurements indicated no long range ordering down to 2 K and the observed effective magnetic moment per Gd3+ ion and the Weiss constant are 7.91 µB and 0.38 K, respectively.

Superionic conduction in ß-eucryptite: inelastic neutron scattering and computational studies.

ß-Eucryptite (LiAlSiO4) is known to show super-ionic conductivity above 700 K. We performed inelastic neutron scattering measurements in ß-eucryptite over 300-900 K and calculated the phonon spectrum using classical molecular dynamics (MD) simulations. The MD simulations were used to interpret the inelastic neutron spectra at high temperatures. The calculated diffusion coefficient for Li showed superionic conduction above 1200 K in the perfect crystal. The presence of defects was found to enhance diffusion and lower the temperature for Li diffusion. The calculated trajectory of Li atoms at higher temperatures shows that preferential movement of the Li atom is along the hexagonal c-axis, which is further confirmed by the ab initio calculated activation energy profile for cooperative lithium ion displacements. The inter- and intra-channel correlated motion of Li along the hexagonal c-axis gives the minimum energy pathway for Li ion conduction in LiAlSiO4.

Structural Stability and Anharmonicity of Pr2Ti2O7: Raman Spectroscopic and XRD Studies.

Herein we report results of pressure- and temperature-dependent Raman scattering studies on Pr2Ti2O7. Pressure-dependent studies performed up to 23 GPa suggest a reversible phase transition above 15 GPa with subtle changes. Temperature-dependent investigations performed in the range of 77-1073 K showed anomalous temperature dependence of some of the Raman modes. Temperature-dependent X-ray diffraction data indicated no structural transition but nonlinear expansion of unit-cell parameters with increasing temperature. With increasing temperature, the structure dilates anisotropically, and volume of coordination polyhedra around all the atoms expands. Also with increasing temperature the distortions in coordination polyhedra around all the atoms decrease, and appreciable decrease is observed in Pr(1)O10 and Pr(3)O9 units. The pressure evolution of Raman-mode frequencies was analyzed for both ambient as well as high-pressure phases, and mode Grüneisen parameters for ambient pressure phase were obtained. The temperature evolution of Raman-mode frequencies was analyzed to obtain the explicit and implicit anharmonic components, and it was found that some of the modes attributable to TiO6 octahedra and PrOn polyhedra have dominating explicit anharmonic component. Comparison of the structural data with the temperature dependence of Raman modes suggests that the anomalous behavior in Raman modes is due to phonon-phonon interaction.

Experimental and Theoretical Investigations on Structural and Vibrational Properties of Melilite-Type Sr2ZnGe2O7 at High Pressure and Delineation of a High-Pressure Monoclinic Phase.

We report a combined experimental and theoretical study of melilite-type germanate, Sr2ZnGe2O7, under compression. In situ high-pressure X-ray diffraction and Raman scattering measurements up to 22 GPa were complemented with first-principles theoretical calculations of structural and lattice dynamics properties. Our experiments show that the tetragonal structure of Sr2ZnGe2O7 at ambient conditions transforms reversibly to a monoclinic phase above 12.2 GPa with ∼1% volume drop at the phase transition pressure. Density functional calculations indicate the transition pressure at ∼13 GPa, which agrees well with the experimental value. The structure of the high-pressure monoclinic phase is closely related to the ambient pressure phase and results from a displacive-type phase transition. Equations of state of both tetragonal and monoclinic phases are reported. Both of the phases show anisotropic compressibility with a larger compressibility in the direction perpendicular to the [ZnGe2O7](2-) sheets than along the sheets. Raman-active phonons of both the tetragonal and monoclinic phases and their pressure dependences were also determined. Tentative assignments of the Raman modes of the tetragonal phase were discussed in the light of lattice dynamics calculations. A possible irreversible second phase transition to a highly disordered or amorphous state is detected in Raman scattering measurements above 21 GPa.

Enhancing the PEC Efficiency in the Perspective of Crystal Facet Engineering and Modulation of Surfaces.

Generation of hydrogen is one of the most promising routes to harvest solar energy for its sustainable utilization. Among different routes, the photoelectrochemical (PEC) process to split water using solar light to produce hydrogen is the green method to generate hydrogen. The sluggish kinetics through complicated pathways makes the oxygen evolution reaction the rate limiting step of the overall water splitting process. Therefore, development of an efficient photoanode for the sustainable oxidation of water is most challenging in an efficient overall PEC water splitting process. The low solar to hydrogen conversion efficiency arises from the slow surface kinetics, poor hole diffusion, and fast charge recombination processes. There have been strategies to improve catalytic performances through the removal of such detrimental effects. The generation of engineered surfaces is one of the important strategies recently adopted for the enhancement of the catalytic efficiencies. The present review has been focused on the discussion of engineered surfaces using crystal facet engineering, protective surface layer, passivation using the atomic layer deposition (ALD) technique, and cocatalyst modified surfaces to enhance the catalytic efficiency. Some of the important parameters defining catalyst performance are also discussed at the beginning of the review.

Dual catalytic activity of a cucurbit[7]uril-functionalized metal alloy nanocomposite for sustained hydrogen generation: hydrolysis of ammonia borane and electrocatalysts for the hydrogen evolution reaction.

H2 is one of the most attractive fuel alternatives to the existing fossil fuels that cause detrimental environmental issues. Thus, there has been an upsurge in the research on the production of green hydrogen. In this view, cucurbit[7]uril (CB7)-functionalized Co:Ni alloy nanocomposites with different compositions, reported here for the first time, were synthesized to synergise the catalytic activities of a nanoalloy and CB7 and screened for hydrogen generation via hydrolysis of ammonia borane (AB). The (Co85:Ni15)50:(CB7)50 nanocomposite exhibited enhanced catalytic performance for AB hydrolysis even at room temperature as compared to the nanoalloy without CB7. Efficient release of ammonia-free green H2 is ensured by the retention of NH3 by the surface functionalized CB7 macrocycles. For sustained release, a novel and cost-effective procedure was used to regenerate AB from the by-product, and the H2 release activity was verified to be on par with commercial AB. The used nanocomposite magnetically separated from the by-product solution was shown to be an efficient electrochemical catalyst for the hydrogen evolution reaction (HER). The cucurbit[7]uril-functionalized Co:Ni nanocomposite demonstrates remarkable dual catalytic performance to generate clean hydrogen from both the hydrolysis of AB at room temperature and the electrochemical HER, thus opening new avenues in supramolecular chemistry for developing noble metal-free catalysts with high activity and long-term stability.

Exploitation of nano alumina for the chromatographic separation of clinical grade 188Re from 188W: a renaissance of the 188W/188Re generator technology.

The (188)W/(188)Re generator using an acidic alumina column for chromatographic separation of (188)Re has remained the most popular procedure world over. The capacity of bulk alumina for taking up tungstate ions is limited (∼50 mg W/g) necessitating the use of very high specific activity (188)W (185-370 GBq/g), which can be produced only in very few high flux reactors available in the world. In this context, the use of high-capacity sorbents would not only mitigate the requirement of high specific activity (188)W but also facilitate easy access to (188)Re. A solid state mechanochemical approach to synthesize nanocrystalline γ-Al(2)O(3) possessing very high W-sorption capacity (500 mg W/g) was developed. The structural and other investigations of the material were carried out using X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer Emmett Teller (BET) surface area analysis, thermogravimetric-differential thermal analysis (TG-DTA), and dynamic light scattering (DLS) techniques. The synthesized material had an average crystallite size of ∼5 nm and surface area of 252 ± 10 m(2)/g. Sorption characteristics such as distribution ratios (K(d)), capacity, breakthrough profile, and elution behavior were investigated to ensure quantitative uptake of (188)W and selective elution of (188)Re. A 11.1 GBq (300 mCi) (188)W/(188)Re generator was developed using nanocrystalline γ-Al(2)O(3), and its performance was evaluated for a period of 6 months. The overall yield of (188)Re was >80%, with >99.999% radionuclidic purity and >99% radiochemical purity. The eluted (188)Re possessed appreciably high radioactive concentration and was compatible for the preparation of (188)Re labeled radiopharmaceuticals.

Gas-phase photooxidation of alkenes by V-doped TiO2-MCM-41: mechanistic insights of ethylene photooxidation and understanding the structure-activity correlation.

Nanoparticles of Ti(0.95)V(0.05)O(2) were found to be impregnated in the hexagonal channels of the MCM-41 host, with a distribution of some particles on the surface, thus leading to an effective variation in the particle size as a function of loading host MCM-41 matrix. These catalysts were subjected to the photocatalytic degradation of alkenes under the ambient conditions in which the photocatalytic activity varied as a function of the loading percentage of Ti(0.95)V(0.05)O(2) in the host MCM-41.This is explained in light of the structure-activity correlation, and the better catalytic activity can be attributed to an electronic interaction between the host and guest molecules, as established from X-ray photoelectron spectroscopy. To understand the mechanistic aspect of the photooxidation of ethylene on the vanadium-doped titania dispersed in the MCM-41 matrix, extensive in situ FTIR experiments were undertaken. The intermediate species produced on bare Ti(0.95)V(0.05)O(2) are different from that produced on the Ti(0.95)V(0.05)O(2)/MCM-41 surface. Moreover, different intermediates were produced during ethylene oxidation under UV and visible irradiation, thus leading to different rates. The ethylene decomposition over bare Ti(0.95)V(0.05)O(2) occurs by means of formation of ethoxy groups, transformed to acetaldehyde or enolates, subsequently to acetates, and then to CO(2) under both UV and visible irradiation. However, in the case of Ti(0.95)V(0.05)O(2)/MCM-41 catalyst with UV irradiation, the adsorbed acetaldehyde thus formed undergoes aldol condensation over the Lewis acid sites to lead to the formation of crotonaldehyde, which is subsequently oxidized to acetate and consequently to CO(2). It was observed that during visible irradiation labile ethyl acetate is produced either by the Tischenko reaction or by the reaction between the labile acetic acid and the unreacted ethoxy groups. The ethyl acetate produces acetic acid monomer, which is oxidized to CO(2). Furthermore, in this work the effects of particle size on the intermediate species were also studied.

Room temperature ferromagnetism in Ce(1-x)Fe(x)O(2-delta) (x = 0.0, 0.05, 0.10, 0.15 and 0.20) nanoparticles synthesised by combustion method.

Nanocrystalline Ce(1-x)Fe(x)O(2-delta) particles with different Fe concentrations (x = 0.0, 0.05, 0.10, 0.15, and 0.20) have been prepared by a gel-combustion method. X-ray diffraction data revealed the formation of an impurity free Ce(1-x)Fe(x)O(2-delta) products up to x = 0.15. This observation is further confirmed from the detailed studies conducted on 10 at.% Fe doped CeO2 using High-Resolution Transmission Electron Microscopy (HRTEM) imaging, Selected-Area Electron Diffraction (SAED) and Raman spectroscopy. DC magnetization studies as a function of field and temperature indicate that they are ferromagnetic with Curie temperature (Tc) well above room temperature.

Room temperature exciton formation in SnO2 nanocrystals in SiO2:Eu matrix: quantum dot system, heat-treatment effect.

SnO2 nanocrystals in SiO2:Eu matrix have been prepared at a relatively low temperature of 170 degrees C for 4 h. Selective transition probability of Eu3+ emission could be done after a suitable excitation wavelength. The room temperature exciton formation at 285 nm for as-prepared nanoparticles is observed and this gives the Bohr's radius of 1.4 nm. Exciton formation disappears for the nanoparticles heated at 500 and 900 degrees C. This is related to the increase in particle size with heat-treatment. A wide-band-gap (4.35 eV) quantum dots is obtained and will be important in photonics and UV-lasing application.

Eu3+ and Dy3+ doped YPO4 nanoparticles: low temperature synthesis and luminescence studies.

Eu3+ and Dy3+ doped YPO4 nanoparticles dispersible in methanol/water were prepared by the reaction of Y3+ and Eu3+/Dy3+ ions with ammonium dihydrogen phosphate in ethylene glycol medium at 160 degrees C. Nature and extent of strain associated with lattice has been found to change with incorporation of Eu3+/Dy3+ ion in the nanoparticles as well as the heat treatment temperature. Based on the TEM studies, it has been established that particles are highly crystalline with an average particle size of around 5 nm. Co-doping YPO4:Eu nanoparticles with Dy3+ ions followed by annealing them at high temperature (900 degrees C) lead to reduction in both Eu3+ and Dy3+ luminescence intensities from the sample and this has been attributed to the clustering effect of the lanthanide ions.

Water dispersible Fe3O4 nanoparticles carrying doxorubicin for cancer therapy.

Water dispersible Fe3O4 nanoparticles (coated with Poly Vinyl Pyrolidone (PVP) and Poly oxy ethylene 25-propylene glycol stearate (POES)) and complexed with Doxorubicin has been prepared and characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The antitumor activity of these particles has been studied by targeting the complex to the tumor site, using an externally applied magnetic field, after oral administration of the magnetic nanoparticle-drug complexes. Our results reveal that the chemotherapy effect of Doxorubicin could be considerably enhanced by combination of the application of the drug-conjugated magnetic Fe3O4 nanoparticles, which are biocompatible and stable, and targeted drug delivery with a magnet. The present report provides the first evidence for the promising application of this novel approach with PVP coated Fe3O4 nanoparticles for cancer therapy using an in vivo murine model.

A rapid method for the synthesis of nitrogen doped TiO2 nanoparticles for photocatalytic hydrogen generation.

A facile, fast, and economic method of doping TiO2, synthesized by conventional precipitation route with N has been developed. By this method, stable N doped TiO2 can be prepared within a short duration of time. The method adopted was to treat the TiO2 powder synthesized by simple precipitation with trioctyl amine (TOA) at 320 degrees C for 2 hours followed by calcination at 400 degrees C for 2 hours to obtain the N-doped TiO2. The sample along with NiO as co-catalyst showed significant photocatalytic activity for hydrogen generation from aqueous methanol solution under sunlight type irradiation. This synthesis method opens up a fast and easy route for doping the existing TiO2 or other wide band gap oxide semiconductors with nitrogen so that they can exhibit enhanced photocatalytic activity under solar irradiation.

Rare earth indates (RE: La-Yb): influence of the synthesis route and heat treatment on the crystal structure.

Rare earth indates are an interesting class of compounds with rich crystallography. The present study explores the crystallographic phases observed in REInO3 (RE: La-Yb) systems and their dependence on synthesis routes and annealing temperature. All REInO3 compositions were synthesized by a solid state route as well as gel-combustion synthesis (GC) followed by annealing at different temperatures. The systems were well characterized by powder XRD studies and were analysed by Rietveld refinement for the structural parameters. The cell parameters were observed to decrease in accordance with the trend in ionic radii on proceeding from lighter to heavier rare earth ions. Interestingly, the synthesis route and the annealing temperature had a profound bearing on the phase relationships observed in the REInO3 series. The solid state synthesized samples depicted an orthorhombic phase (Pbnm) field for LaInO3 to SmInO3, followed by a hexagonal-type phase (P63cm) for GdInO3 to DyInO3. However, the phase field distribution was greatly influenced upon employing gel-combustion (GC) wherein both single-phasic hexagonal and orthorhombic phase fields were found to shrink. Annealing the GC-synthesized compositions to still higher temperatures (1250 °C) further evolved the phase boundaries. An important outcome of the study is observance of polymorphism in SmInO3 which crystallized in the hexagonal phase when synthesized by GC and orthorhombic phase by solid state synthesis. This reveals the all-important role played by synthesis conditions. The existence and energetics of the two polymorphs have been elucidated and discussed with the aid of theoretical studies.

Preparation and crystal structure of K2Ce(PO4)2: a new complex phosphate of Ce(iv) having structure with one-dimensional channels.

In this manuscript we report crystal structure of a new complex binary phosphate K2Ce(4+)(PO4)2 in K2O-P2O5-CeO2 system prepared by solid state reaction at moderate temperature conditions. The prepared material was characterized by powder X-ray diffraction using lab source and synchrotron radiation as well as thermal analyses, Raman scattering, FTIR, and X-ray photoelectron spectroscopic studies. The crystal structure of the compound has been determined from powder XRD data by ab initio structure solution in direct space followed by Rietveld refinements. K2Ce(PO4)2 crystallizes in a monoclinic (P21/n) lattice with unit cell parameters: a = 9.1060(4), b = 10.8160(5), c = 7.6263(4) Å, ß = 111.155(2)°, V = 700.50(6) Å(3). The unit cell contains two distinguishable PO4 tetrahedra and one CeO8 distorted square anti-prism. Raman spectroscopy confirmed the presence of isolated PO4(3-) groups in the structure. These PO4 tetrahedra are connected to one CeO8 polyhedra by sharing one edge and three other CeO8 polyhedra by sharing corners to form the three dimensional structure and empty channels parallel to a-axis. The channels are occupied by two crystallographically distinguishable K(+) ions which maintain the charge neutrality. Contrast to the earlier reported composition K4Ce2P4O15, this study revealed the composition in actual is K4Ce2P4O16 with Ce in 4+ oxidation state and is also supported by X-ray photoelectron spectroscopic and X-ray absorption near edge structure studies. Differential scanning calorimetric studies revealed a structural transition around 525 °C which reverts on cooling with a large thermal hysteresis. At higher temperature it undergoes a loss of oxygen atom and subsequently loss of phosphorus as P2O5. These thermal effects are also supported by in situ high temperature XRD studies. Finally the crystal chemistry of complex phosphates with tetravalent cations is also discussed.