Non-monotonic size dependence of the elastic modulus of nanocrystalline ZnO embedded in a nanocrystalline silver matrix

We present the first high pressure Raman study on nanocrystalline ZnO films with different average crystallite sizes. The problem of low Raman signals from nano sized particles was overcome by forming a nanocomposite of Ag and ZnO nanoparticles. The presence of the nanodispersed Ag particles leads to a substantial surface enhancement of the Raman signal from ZnO. We find that the elastic modulus of nanocrystalline ZnO shows a non-monotonic dependence on the crystallite size. We suggest that the non-monotonicity arises from an interplay between the elastic properties of the individual grains and the intergranular region.Comment: 10 pages, 6 figure

High Pressure phase transitions in BaWO4

Using in-situ angle dispersive x-ray diffraction, we have shown that barium tungstate, which exists in scheelite phase at ambient conditions, transforms to a new phase about seven giga pascal. Analysis of our data based on Le bail refinement suggests that this phase could be fergusonite and not mercuric molybdate type, which was proposed earlier from the Raman investigations. Beyond fourteen giga pascal this compound undergoes another phase transformation to a significantly disordered structure. Both the phase transitions are found to be reversible.Comment: 14 pages with 4 figures and 1 tabl

An Investigation of the Pressure-Induced Structural Phase Transition of Nanocrystalline α-CuMoO4

The structural behavior of nanocrystalline α-CuMoO4 was studied at ambient temperature up to 2 GPa using in situ synchrotron X-ray powder diffraction. We found that nanocrystalline α-CuMoO4 undergoes a structural phase transition into γ-CuMoO4 at 0.5 GPa. The structural sequence is analogous to the behavior of its bulk counterpart, but the transition pressure is doubled. A coexistence of both phases was observed till 1.2 GPa. The phase transition gives rise to a change in the copper coordination from square-pyramidal to octahedral coordination. The transition involves a volume reduction of 13% indicating a first-order nature of the phase transition. This transformation was observed to be irreversible in nature. The pressure dependence of the unit-cell parameters was obtained and is discussed, and the compressibility analyzed

Raman and X-ray diffraction investigations on BaMoO<SUB>4</SUB> under high pressures

X-ray diffraction and Raman scattering studies on the scheelite structured barium molybdate show that, at ~5.8 GPa, it undergoes a first order phase transition to the fergusonite structure (I 2/a,Z=4)-as also observed in iso-structural barium tungstate. At still higher pressures, barium molybdate transforms to another phase between ~7.2 and 9.5 GPa. On release of pressure from 15.8 GPa, the initial phase is recovered, implying that the observed structural modifications are reversible

An Investigation of the Pressure-Induced Structural Phase Transition of Nanocrystalline alpha-CuMoO4

The structural behavior of nanocrystalline α-CuMoO4 was studied at ambient temperature up to 2 GPa using in situ synchrotron X-ray powder diffraction. We found that nanocrystalline α-CuMoO4 undergoes a structural phase transition into γ-CuMoO4 at 0.5 GPa. The structural sequence is analogous to the behavior of its bulk counterpart, but the transition pressure is doubled. A coexistence of both phases was observed till 1.2 GPa. The phase transition gives rise to a change in the copper coordination from square-pyramidal to octahedral coordination. The transition involves a volume reduction of 13% indicating a first-order nature of the phase transition. This transformation was observed to be irreversible in nature. The pressure dependence of the unit-cell parameters was obtained and is discussed, and the compressibility analyzed

Pressure-induced phase transitions in Al<SUB>2</SUB>(WO<SUB>4</SUB>)<SUB>3</SUB>

The high pressure behavior of aluminum tungstate [Al2(WO4)3] has been investigated up to ~18 GPa with the help of Raman scattering studies. Our results confirm the recent observations of two reversible phase transitions below 3 GPa. In addition, we find that this compound undergoes two more phase transitions at ~5.3 and ~6 GPa before transforming irreversibly to an amorphous phase at ~14 GPa

Pressure-Induced Structural Phase Transition of Co-Doped SnO₂ Nanocrystals

Co-doped SnO2 nanocrystals (with a particle size of 10 nm) with a tetragonal rutile-type (space group P42/mnm) structure have been investigated for their use in in situ high-pressure synchrotron angle dispersive powder X-ray diffraction up to 20.9 GPa and at an ambient temperature. An analysis of experimental results based on Rietveld refinements suggests that rutile-type Co-doped SnO2 undergoes a structural phase transition at 14.2 GPa to an orthorhombic CaCl2-type phase (space group Pnnm), with no phase coexistence during the phase transition. No further phase transition is observed until 20.9 GPa, which is the highest pressure covered by the experiments. The low-pressure and high-pressure phases are related via a group/subgroup relationship. However, a discontinuous change in the unit-cell volume is detected at the phase transition; thus, the phase transition can be classified as a first-order type. Upon decompression, the transition has been found to be reversible. The results are compared with previous high-pressure studies on doped and un-doped SnO2. The compressibility of different phases will be discussed

Heck-type olefination and Suzuki coupling reactions using highly efficient oxacalix[4]arene wrapped nanopalladium catalyst

A simple one-pot method is used for the synthesis of water dispersible and stable palladium nanoparticles (PdNps) where oxacalix[4]arene dihydrazide (OXDH) is used as both a reducing and capping agent. The OXDH-PdNps have been characterized by UV–Visible spectroscopy, Fourier transform infrared (FT-IR), transmission electron microscopy (TEM), energy‐dispersive X‐ray spectroscopy (EDX), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The OXDH-PdNps are spherical in shape with an average size of 3–4 nm and well crystallized in a face centered cubic structure. The capping of the OXDH ligand on the nanoparticles surface was evaluated using FT-IR. The OXDH-PdNps have been used in carbon–carbon coupling reactions, namely, the Suzuki–Miyaura and Mizoroki–Heck reactions. Both of the reactions are carried out under phosphine-free conditions to provide better yields. The nanocatalyst can be easily recovered and reused for six consecutive catalytic cycles without any significant loss in its catalytic activity. Keywords: Palladium nanoparticles, Oxacalixarene, Suzuki–Miyaura’s reaction, C-C cross coupling reaction, Heck reactio