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Structural stability of a transparent conducting oxide CuLaO2 at high pressures is investigated using in-situ Raman spectroscopy, electrical resistance, and x-ray diffraction techniques. The present Raman investigations indicate a sequence of structural phase transitions at 1.8 GPa and 7GPa. The compound remains in the first high pressure phase when pressure is released. Electrical resistance measurements carried out at high pressures confirm the second phase transition. These observations are further supported by powder x-ray diffraction at high pressures which also showed that a-axis is more compressible than c-axis in this compound. Fitting the pressure dependence of unit cell volume to 3rd order Birch-Murnaghan equation of state, zero pressure bulk modulus of CuLaO2 is determined to be 154(25) GPa. The vibrational properties in the ambient delafossite phase of CuLaO2 are investigated using ab-initio calculations of phonon frequencies to complement the Raman spectroscopic measurements. Temperature dependence of the Raman modes of CuLaO2 is investigated to estimate the anharmonicity of Raman modes. © 2014 AIP Publishing LLC. [ABSTRACT FROM AUTHOR]

The effect of pressure on the vibrational properties of bulk and nanocrystalline powders of cubic bixbyite-type In2O3 has been investigated at room temperature by means of Raman spectroscopy up to 31.6 and 30 GPa, respectively. We have been able to follow the pressure dependence of up to sixteen and seven Raman modes in bulk and nanocrystalline cubic In2O3, respectively. The experimental frequencies and pressure coefficients of the Raman-active modes of bulk cubic In2O3 at ambient pressure are in good agreement with those predicted by our theoretical ab initio calculations. Furthermore, a comparison of our experimental data with our calculations for the Raman modes in rhombohedral corundum and orthorhombic Rh2O3-II structures and with already reported Raman modes of rhombohedral corundum-type In2O3 at room pressure indicate that Raman scattering measurements provide no experimental evidence of the cubic to rhombohedral or cubic to orthorhombic phase transitions either in bulk material or in nanocrystals up to 30 GPa. [ABSTRACT FROM AUTHOR]

Synthesis of Mo-substituted CeVO4 systems by facile co-precipitation process is reported wherein an upper solubility limit of 40 mol% Mo was obtained retaining the tetragonal structure. Solid solution formation was investigated by X-ray diffraction, X-ray fluorescence and Raman spectroscopy and XPS. Introduction of Mo into the anionic framework yielded hierarchical mesoporous structures with substantial increase in surface area from 76 to 147 m2/g as exhibited by TEM and BET analysis. Complete uptake of Pb2+ ions from aqueous solutions was shown by both CeVO4 and Mo-CeVO4 with sorption capacity of 100 mg/g. In addition, the presence of Mo in CeVO4 depicted five times faster and superior kinetics than pure CeVO4. Various isotherms have been used to model the data. This study not only unravels the structural aspects of Mo-substituted CeVO4 system but also discusses new promising sorbents for toxic Pb2+ ions obtained by simple synthetic route. [ABSTRACT FROM AUTHOR]

In this paper we report a new high-pressure rhombohedral phase of Ce2Zr2O8 observed in high-pressure angle-dispersive x-ray diffraction and Raman spectroscopy studies up to nearly 12 GPa. The ambient-pressure cubic phase of Ce2Zr2O8 transforms to a rhombohedral structure beyond 5 GPa with a feeble distortion in the lattice. The pressure evolution of the unit-cell volume showed a change in compressibility above 5 GPa. The unit-cell parameters of the high-pressure rhombohedral phase at 12.1 GPa are ah = 14.6791(3) Å, ch = 17.9421(5) Å, and V = 3348.1(1) Å3. The structure relations between the parent cubic (P213) and rhombohedral (P32) phases were obtained via group-subgroup relations. All the Raman modes of the cubic phase showed linear evolution with pressure, with the hardest one at 197 cm-1. Some Raman modes of the high-pressure phase have a non-linear evolution with pressure, and softening of one low-frequency mode with pressure is found. The compressibility, equation of state, and pressure coefficients of Raman modes of Ce2Zr2O8 are also reported. [ABSTRACT FROM AUTHOR]

Structural stability of HfW2O8 is investigated at high pressure using Raman spectroscopy. Irreversible amorphization is found to occur when pressurized to above 3 GPa under hydrostatic conditions. The Raman spectrum of the pressure-amorphized sample closely resembles that of amorphous WO3. On the other hand, spectrum of the recovered sample subjected to uniaxial compression of about 5 GPa showed bands characteristic of crystalline HfO2 besides the parent cubic phase and amorphous phase. Ex situ x-ray diffraction measurements on the pressure-cycled samples also indicated the presence of monoclinic HfO2. These results suggest that the observed pressure-induced amorphization (PIA) under hydrostatic compression is indeed due to hindered decomposition, which is facilitated under uniaxial compression. Thus, the behavior of HfW2O8 appears to be different from that of ZrW2O8, which exhibited only PIA and not pressure-induced decomposition at ambient temperature. [ABSTRACT FROM AUTHOR]

The phase relations in CeO2-Ho2O3 and CeO2-Er2O3 systems have been established under the slow-cooled conditions. As per x-ray diffraction (XRD), in both the series a single-phasic solid solution forms up to the nominal composition Ce0.6RE0.4O1.8 (RE=Ho, Er) retaining the F-type structure of parent ceria. In Ce1-xErxO2-x/2 system the presence of microdomains of C-type phase have been revealed by Raman spectroscopy for composition x=0.4, which has been identified as single phasic by XRD. Photoluminescence studies also show that biphasic region commences from x=0.4 for Ce1-xHoxO2-x/2 series. The biphasicity continues until x=0.7 for both the series. From x=0.8 the solid solutions exist as C-type single phasic, which is isotypic to another end member RE2O3 (RE=Ho, Er) and as revealed by both XRD and Raman spectroscopy. High temperature XRD studies show that no temperature induced phase change has been observed in either of the series until 1273 K. In this work photoluminescence data was used to delineate the phase boundary. [ABSTRACT FROM AUTHOR]

Controlled boron doping of diamond film using nontoxic reagents is a challenge in itself. During the present study, attempts have been made to dope diamond films in situ with boron from a solution of boric acid (H3BO3) in methanol (CH3OH) using a specially designed bubbler that ensured continuous and controlled flow of vapors of boron precursors during deposition. The samples are thoroughly characterized using a host of techniques comprising of x-ray photoelectron spectroscopy, Raman, x-ray diffraction, and current-voltage measurements (I-V). Cross-sectional micro-Raman spectroscopy has been used to obtain depth profile of boron in diamond films. Boron concentration ([B]) in the films is found to vary linearly on a semilog scale with molarity (M) of H3BO3 in CH3OH. Lattice constant of our samples is smaller than the reported American society for testing and materials (ASTM) values due to oxygen incorporation and it increases with [B] in the diamond samples. Heavily boron doped samples exhibit Fano deformation of the Raman line shape and negative and/zero activation barrier in temperature dependent I-V measurements that indicate the formation of metallic phase in the samples. The present study illustrates the feasibility of safe and controlled boron doping of diamond films using a solution of H3BO3 in CH3OH over a significant range of [B] from semiconductor to metallic regime but with a little adverse effect due to unintentional but unavoidable incorporation of oxygen. [ABSTRACT FROM AUTHOR]

In the present study, x-ray diffraction, Raman spectroscopy, spectroscopic ellipsometry, photoluminescence, and x-ray photoelectron spectroscopy techniques were used to study the effect of 120 MeV [sup 107]Ag[sup 9+] ion irradiation on nanocrystalline Cu[sub 2]O thin films grown by the activated reactive evaporation technique. The influence of dense electronic excitations during ion irradiation on the structural and optical properties of the Cu[sub 2]O thin films was studied. Experimental results demonstrate that the phase and the size of nanocrystallites in the Cu[sub 2]O thin films as well as associated surface states can be tailored by controlling ion fluence. The Cu[sub 2]O higher symmetry cubic phase is observed to be quite stable under a higher temperature and irradiation-induced thermal spikes, which accompanies ion irradiation. [ABSTRACT FROM AUTHOR]

The radiation-resistant response of BaTiO3 in the tetragonal and rhombohedral phases on exposure to 100 MeV Ag7+ ion irradiation was investigated by in situ X-ray diffraction (XRD) at room temperature (300 K) and low temperature (25 K), respectively. This study revealed that the BaTiO3 in rhombohedral phase retained crystallinity up to an ion fluence of 1×1014 ions/cm2, whereas tetragonal phase amorphized at much lower fluence viz. 1×1013 ions/cm2. The in situ XRD along with Raman spectroscopy studies revealed that BaTiO3 in rhombohedral phase is more radiation resistant than that of tetragonal phase. The density functional theory ( DFT) calculations confirmed higher bond strength of rhombohedral phase as compared to tetragonal phase, which supported the experimental result of higher radiation stability of rhombohedral phase. The theoretical predictions on high-temperature phase will be of relevance to the nuclear waste applications. [ABSTRACT FROM AUTHOR]

Raman forbidden modes and surface defect-related Raman features in SnO2 nanostructures carry information about disorder and surface defects which strongly influence important technological applications like catalysis and sensing. Because of the weak intensities of these peaks, it is difficult to identify these features by using conventional Raman spectroscopy. Tip enhanced Raman spectroscopy (TERS) studies conducted on SnO2 nanoparticles (NPs) of size 4 and 25nm have offered significant insights of prevalent defects and disorders. Along with one order enhancement in symmetry allowed Raman modes, new peaks related to disorder and surface defects of SnO2 NPs were found with significant intensity. Temperature-dependent Raman studies were also carried out for these NPs and correlated with the TERS spectra. For quasi-quantum dot sized 4-nmNPs, the TERS study was found to be the best technique to probe the finite size-related Raman forbidden modes. [ABSTRACT FROM AUTHOR]

A new series of Pr1−xCexScO3 (0.0 ≤x≤ 1.0) compounds was synthesized by a two-step synthesis route, involving a combustion reaction followed by reduction while heating in a low partial pressure of O2, generated by a zirconium sponge that acts as an oxygen getter. For the first time, perovskite solid solution formation was observed in this series in the entire homogeneity range. These compounds were characterized using XRD, Raman spectroscopy and DRUV-visible spectroscopy. Rietveld refinement was carried out on the XRD data to determine unit cell parameters, bond lengths, bond angles along with the tilt angles for ScO6 octahedra. The analyses of the Raman shift were also in agreement with the XRD data. All compounds in this series showed a decreasing trend in the bandgap from 4.74 to 2.91 eV as a function of increasing Ce3+ concentration. [ABSTRACT FROM AUTHOR]

The localized effect of impurities in single GaN nanowires in the sub-diffraction limit is reported using the study of lattice vibrational modes in the evanescent field of Au nanoparticle assisted tip enhanced Raman spectroscopy (TERS). GaN nanowires with the O impurity and the Mg dopants were grown by the chemical vapor deposition technique in the catalyst assisted vapor-liquid-solid process. Symmetry allowed Raman modes of wurtzite GaN are observed for undoped and doped nanowires. Unusually very strong intensity of the non-zone center zone boundary mode is observed for the TERS studies of both the undoped and the Mg doped GaN single nanowires. Surface optical mode of A1 symmetry is also observed for both the undoped and the Mg doped GaN samples. A strong coupling of longitudinal optical (LO) phonons with free electrons, however, is reported only in the O rich single nanowires with the asymmetric A1(LO) mode. Study of the local vibration mode shows the presence of Mg as dopant in the single GaN nanowires. [ABSTRACT FROM AUTHOR]

Fabrication of wear resistant and lowfriction carbon films on the engineered substrates is considered as a challenging task for expanding the applications of diamond-like carbon (DLC) films. In this paper, pulsed laser deposition (PLD) technique is used to deposit DLC films on two different types of technologically important class of substrates such as silicon and AISI 304 stainless steel. Laser power density is one of the important parameter used to tailor the fraction of sp2 bonded amorphous carbon (a-C) and tetrahedral amorphous carbon (ta-C) made by sp3 domain in the DLC film. The I(D)/I(G) ratio decreases with the increasing laser power density which is associated with decrease in fraction of a-C/ta-C ratio. The fraction of these chemical components is quantitatively analyzed by EELS which is well supported to the data obtained from the Raman spectroscopy. Tribological properties of the DLC are associated with chemical structure of the film. However, the super lowvalue of friction coefficient 0.003 is obtained when the film is predominantly constituted by a-C and sp2 fraction which is embedded within the clusters of ta-C. Such a particular film with super low friction coefficient is measured while it was deposited on steel at low laser power density of 2 GW/cm2. The super low friction mechanism is explained by low sliding resistance of a-C/sp2 and ta-C clusters. Combination of excellent physical and mechanical properties of wear resistance and super low friction coefficient of DLC films is desirable for engineering applications. Moreover, the high friction coefficient of DLC films deposited at 9GW/cm2 is related to widening of the intergrain distance caused by transformation from sp2 to sp3 hybridized structure. [ABSTRACT FROM AUTHOR]

In this article, we report the structural phase transitions in Bi4 V2 O11 as observed from temperature-dependent Raman scattering and X-ray diffraction measurements. Four different types of highly disordered coordination polyhedra around the vanadium atoms with large dispersion of V-O bond lengths are observed in Bi4 V2 O11 at ambient temperature. The observed V-O bond lengths could be grouped into two categories, viz. shorter <1.7 Å and longer >1.7 Å. The Raman modes of Bi4 V2 O11 could be assigned to vibration of these bonds and V-O-V linkages. We could correlate the difference in degree of anharmonicity of the phonon modes with temperature to differences in V-O bond strength. The local structure of vanadium-oxygen network in Bi4 V1.8 Cu0.2 O10.7 was also obtained by similar studies. The effect of highly disordered anion sublattice in the doped compound is reflected in the broadening of the Raman modes. [ABSTRACT FROM AUTHOR]

We report the vibrational properties of vertical and oblique InN nanorods (NRs) grown by molecular beam epitaxy (MBE). Surface optical (SO) Raman mode at 561 cm−1, belonging to E1 symmetry [SO( E1)], is identified along with symmetry allowed Raman modes of E2(low), E2(high), and E1(LO) at 87, 489, and 589 cm−1, respectively, corresponding to wurtzite InN phase. Usually, SO phonon modes arise due to breakdown of translational symmetry of surface potential at surface defects, which are attributed by the surface roughness. Intensity distribution of E1(LO) and SO( E1) phonon modes over a specified area have been analysed using Raman area mapping with an optical resolution of 400 nm. Imaging with E1(LO) phonon mode, originating from the bulk of the sample, distinguishes the vertical NRs alone. We are able to resolve NR morphologies in both vertical and oblique cases with additional Raman mapping analysis of SO( E1) phonon mode, emerging from the surface irregularities, which are confined to the tip of MBE grown NRs. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We report the synthesis of high-quality graphene on Cu foils using hot-filament chemical vapor deposition technique and demonstrate that by suitably varying the CH4 and H2 flow rates, one can also obtain hydrogenated graphene. Micro-Raman spectroscopy studies confirm the growth of monolayer graphene as inferred from the intensity ratio of 2D to G peak which is nearly four in unhydrogenated samples. Detailed Raman area mapping confirms the uniform coverage of monolayer graphene. The grown layer is also transferred onto a Si substrate over ~10 × 10 mm sq. area. The present results provide a leap in synthesis technology of high-quality graphene and pave way for scaling up the process. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Indentation at very low load rate showed region of constant volume with releasing load in crystalline (c-)Si, indicating a direct observation of liquidlike amorphous phase which is incompressible under pressure. Signature of amorphization is also confirmed from load dependent indentation study where increased amount of amorphized phase is made responsible for the increasing elastic recovery of the sample with increasing load. Ex situ Raman study confirmed the presence of amorphous phase at the center of indentation. The molecular dynamic simulation has been employed to demonstrate that the effect of indentation velocities has a direct influence on c-Si during nanoindentation processes. [ABSTRACT FROM AUTHOR]

Chemical vapor deposited diamond films grown on strained gallium nitride-coated quartz substrate are found to display a dominantly hexagonal diamond phase. The phase identification is done using Raman spectroscopy and orientation imaging microscopy (OIM). The presence of a 1324.4 cm-1 band in the Raman spectra is attributed to a hexagonal diamond symmetry, but the unambiguous signature of the hexagonal phase is confirmed by OIM. A phase map of the sample clearly shows that 88% of the scanned sample area is hexagonal diamond. [ABSTRACT FROM AUTHOR]

In situ Raman spectroscopic studies have been carried out on Ag3[Co(CN)6] at high pressures up to 16 GPa. From the pressure dependence of the Raman frequencies, the mode Grüneisen parameters in the trigonal and the monoclinic phases are obtained. Besides the reported trigonal-to-monoclinic transition at 0.2 GPa, it is observed that the compound shows pressure-induced amorphization above 13 GPa. The recovered sample shows features characteristic of amorphous carbon nitride, indicating the decomposition of the parent compound in the pressure-reducing cycle. Temperature dependence of the mode frequencies over the range 80-290 K is also investigated, from which the modes that are more anharmonic than other modes are identified. [ABSTRACT FROM AUTHOR]

CeScO3 was synthesized by a two step synthesis route involving a combustion method followed by vacuum healing at 1100 °C in the presence of Zr sponge which acts as an oxygen getler. The compound was characterized by various techniques such as X-ray diffraction (XRD), high temperature XRD, thermogravimetry, diffuse retlectance (DR)-UV visible spectrophotometry, and Raman spectroscopy. Fluorite-type (F-type) solid solution with composition Ce0.5-Sc0.5O1.75 was observed as an intermediate dedng the synthesis of CeScO3. Only by mere redox reaction was a reversible transformation between tluedte.type structure and perovskites structure observed. ceSco3 was found as semiconducting oxide with band gap of 3.2 eV arising mainly belween Op states in the valence band and Sc d and ce d states in the conduction band with small contributions coming from Ce f and Sc p states. First-principles potential plane-wave-based calculations were performed for the band gap and its origin in CeSco3. Photoluminescence measurement showed that CeScO3 is a potential host material giving broad blue emission. This was further confirmed by demonstrating CeSco3 doped with 2 mol % Tb3+ compound as an efficient green light emitter. [ABSTRACT FROM AUTHOR]

[Display omitted] • CO oxidation is always of great interest owing to its role in pollution abatement. Various supports which have been used for catalysts development have the sintering problem. The novel support CeZrO 4-δ is resistant to sintering compared to pure ceria. CeZrO 4-δ material is least explored and it has a robust structure. • Role of crystallite size in CO oxidation is a topic of debate. But by restricting our studies to 1% Pd loading, we observed that around 7 nm size is optimum for the reaction (100% conversion at 140° C) whereas further increase in Pd crystallite size to 8.5 nm decreases the activity. • In our studies, enhancement in the onset activity was observed in case of reduced catalyst where the support CeZrO 4-δ was deliberately reduced to form anionic vacancies. It clearly reveals the role of Ce3+ on the activity. • Thus by simple photo-deposition technique, we could not only achieve high metal dispersion but also we could fine tune average crystallite size of palladium by changing irradiation time. In nutshell, 7 nm crystallite size and more surface Ce3+ species found to be a suitable combination for CO oxidation reaction. Photodeposited palladium on nanocrystalline CeZrO 4-δ support was evaluated for CO oxidation, as a function of particle size and pre-treatment. All the catalysts were well characterized by XRD, SEM, EDX, TEM, CO chemisorption and Raman spectroscopy. It was observed that change in photodeposition time alters the average crystallite size of Pd, and the same was confirmed by CO chemisorption. 7 nm average crystallite size of Pd exhibited excellent catalytic activity for CO oxidation. In order to understand the effect of support and metal-support interaction, 1 wt% Pd was deposited deliberately onto reduced and oxidized CeZrO 4-δ support. The reduced support with anionic vacancies and more Ce3+ species exhibited an improvement in CO oxidation at onset temperature. Detailed analysis shows that Pd-deposition occurs preferentially at oxygen-vacancy sites and subsequent metal-support interaction influences the catalysis. [ABSTRACT FROM AUTHOR]

Structural and vibrational properties of orthorhombic BaTe2O6, a mixed valence tellurium compound, have been investigated by in situ synchrotron X-ray diffraction (XRD) studies up to 16 GPa and Raman spectroscopy up to 37 GPa using a diamond-anvil cell. The structure of orthorhombic BaTe2O6 has layers of [Te2O6]2-, formed by TeO6 octahedra and TeO5 square pyramids and Ba2+ ions stacked alternately along the 〈010〉 direction. A reversible pressure-induced structural transformation from the ambient orthorhombic (Cmcm) to a monoclinic (P21/m) structure is observed in both XRD and Raman spectroscopic investigations around 10 GPa. Ab initio calculations using density functional theory (DFT) corroborate this phase transition as well as the transition pressure. Both XRD and DFT calculations reveal that the high-pressure monoclinic structure is closely related to the ambient pressure orthorhombic structure, and the transformation is accompanied by a slight rearrangement of the structural units. Pressure evolution of unit cell parameters of the ambient pressure phase reveals an anisotropic compressibility with maximum compression along the b-axis as compared to other crystallographic directions. The bulk modulus and its derivative are found to be B0 = 88(2) GPa and B0 = 4.1(7) from high-pressure experiments, while those calculated by DFT are B0 = 123 GPa and B0' = 4.74. Pressure evolution of Raman spectra indicates significant changes across the orthorhombic to monoclinic phase transformation at 9.1 GPa and no evidence of further structural changes up to 37 GPa. Raman mode frequencies, pressure coefficients, and Grüneisen parameters in the low- and high-pressure phases of BaTe2O6 have been obtained for both monoclinic and orthorhombic phases. Finally, the mechanism for the instability of the orthorhombic phase under pressure is proposed. [ABSTRACT FROM AUTHOR]

Detailed structural and electrical investigations were carried out on an A-site disordered hexagonal Y1-xGdxInO3 (0.0 < x < 1.0) series synthesized by a self-assisted gel-combustion route. The phase relations show profound temperature dependence. The metastable C-type modification could be stabilized for all the compositions, which on further hearing get converted to stable hexagonal polymorphs. The conversion temperature (C-type to hexagonal) was found to increase with an increase in Y3+ content. The system was observed to be single-phasic hexagonal at 1250 °C throughout the composition range. Interestingly, the increase in planar bonds of InOs polyhedra was found to be twice that of the apical bonds on Gd3+ substitution. Careful Raman spectroscopic studies highlighted a definitive though subtle structural change from x = 0.7 onward. The same observation is also corroborated by the dielectric studies. Electric field-dependent polarization measurements showed the ferroelectric hysteresis loop for pure YInO3. The system transforms from ferroelectric in Yln03 to almost paraelectric for GdInOv In the present study, XRD, Raman, and electrical characterizations in conjunction reveal that to tune the electrical properties of the hexagonal rare earth indates, the variation in tilting of InO5 polyhedra has to be influenced, which could not be brought about by isovalent A-site substitution. [ABSTRACT FROM AUTHOR]

Zircon-type PrVO4 and SmVO4 have been studied by high-pressure Raman spectroscopy up to 17 GPa. The occurrence of phase transitions has been detected when compression exceeds 6 GPa. The transformations are not reversible. Raman spectra of the high-pressure phases show similarities with those expected for a monazite-type phase in PrVO4 and a scheelite-type phase in SmVO4.The high-pressure phases have been also synthesized using a large-volume press and recovered at ambient conditions. X-ray diffraction measurements of the metastable products recovered after decompression confirms the monazite (PrVO4) and scheelite (SmVO4) structures of the high-pressure phases. Based upon optical properties of the reported new polymorphs, novel applications for rare-earth vanadates are proposed, including photocatalytic hydrogen production. [ABSTRACT FROM AUTHOR]

The present work involves the synthesis of a series of Sm2−xDyxZr2O7 compounds (0.0 ≤ x ≤ 2.0) by a controlled gel combustion process. The powders were thoroughly analyzed by powder X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy, and diffuse-reflectance UV−visible spectroscopy. The powder XRD studies revealed the system to be single-phasic throughout with retention of pyrochlore-type ordering until 40 mol % of Dy3+, beyond which the pyrochlore lattice gives way to the defect fluorite structure. Interestingly, Raman spectroscopic studies (as against XRD studies) showed retention of pyrochlore-type ordering throughout the homogeneity range of the compositions studied. This is perhaps the first study that reports retention of a weak pyrochlore-type superstructure in the Dy2Zr2O7 system, which was otherwise known to crystallize in the defect fluorite system. The ionic conductivity measurements showed an increase in the activation energy (Ea) with an increase in the mole percent of Dy3+ owing to the decreased mobility with an increase in the degree of disorder. The system possesses a tunable band gap with varying amounts of Dy3+. First-principles calculations were performed to support a decrease in the band gap of the doped system with an increase in the Dy3+ content. The potential as photocatalysts of some of these compositions was explored, and they exhibited high photocatalytic activity for degradation of xylenol orange, with t1/2 increasing from pure Sm2Zr2O7 to pure Dy2Zr2O7. [ABSTRACT FROM AUTHOR]

Variation in degree of disorder and its impact on photocatalytic dye degradation has been studied in Y 2 Sn 2-x Zr x O 7 series. The structural variations of the compositions were thoroughly characterized by X-ray diffraction, Raman spectroscopy, 119Sn MAS NMR, EXAFS and XPS. A phase transition from ordered pyrochlore to disordered fluorite could be observed in the series whilst transiting from Y 2 Sn 2 O 7 to Y 2 Zr 2 O 7 without any signature of presence of bi-phasicity. Formation of a random solid solution phase has been confirmed by 119Sn MAS NMR results. All the compositions until x ​= ​1.0 remain as pyrochlore whereas the compositions with x ​≥ ​1.5 preferentially adopt defect-fluorite structure. X-ray photoelectron spectroscopy clearly demonstrates that the coordination environment Zr and O varies with increase in Zr content, however, the coordination environment of Sn does not alter with substitution. The phase transformation from pyrochlore to defect fluorite occurs at relatively higher Zr rich composition than expected from classical radius ratio rule due to higher covalency present in Sn–O bond. With increase in Zr content in the series crystallite size, surface charge, nature BO 6 octahedra etc. varies and it has been found that these parameters has strong bearing on catalytic property of the materials. A generic understanding for the photocatalytic degradation of cationic methylene blue dye was achieved as a function of structural disordering in the Y 2 Sn 2-x Zr x O 7 system. [Display omitted] • Order-disorder phenomena in pyrochlore has been studied by XRD and Raman Spectroscopy. • 119Sn NMR and XPS could be successfully employed to investigate local structure of pyrochlore. • It has been observed that covalency of Sn–O bond has strong role in extension of stability of pyrochlore phase. • Surface charge, crystallite size, degree of disorder in the system has profound effect on photocatalytic dye degradation. [ABSTRACT FROM AUTHOR]

Abstract: We report here, a detailed study of the parameter window of the deposition pressures to grow the diamond films on GaN coated quartz substrates using microwave plasma deposition technique. Hexagonal GaN films of 5 µm coated on quartz are used as substrates for diamond deposition in the pressure range of 80–140 Torr, using microwave plasma chemical vapor deposition (MPCVD) technique. The diamond films are characterized by scanning electron microscopy, XRD, photoluminescence and Raman spectroscopy. Scanning electron microscope image shows that the nucleation density of the films is high and we can deposit a continuous film for a deposition time ranging for 6–8 h. Oriented growth of diamond has been observed at higher pressure. [Copyright &y& Elsevier]

In situ high-pressure Raman spectroscopy and ab initio calculations are carried out to investigate the phase stability and the thermal expansion behavior of H3[Co(CN)6]. Raman studies at high pressures in a diamond anvil cell identify soft phonons and phase instability at 2.3 GPa. Evidence of pressure-induced amorphization is found at 11 GPa. The phonon frequencies and eigenvectors obtained from ab initio calculation are used to complement the observed phonon spectra and for assignment of Raman modes. The computed eigenvector displacement patterns indicate that the soft modes correspond to the CN-librational vibrations (Eg mode) of the Co-CN-H-NC-Co linkages and their Grüneisen parameters are found to be negative, in agreement with our measured values. The thermal expansion coefficient (15.6×10-6K-1) calculated using our computed mode Grüneisen parameters is found to be in good agreement with the reported value (20×10-6K-1). Temperature-dependent phonon spectra down to 77 K are used to obtain the anharmonicities of different modes. [ABSTRACT FROM AUTHOR]