Pressure Angle Dispersive X-ray Diffraction Research Articles

Engineering ZnO with Cu doping to lower the transition pressure: Experimental and theoretical investigations

Zinc Oxide (ZnO) is an n-type wide bandgap semiconductor. Doping of different elements in ZnO potentially affects its structural, optical and electronic properties. We have carried out high pressure angle dispersive x-ray diffraction and Raman scattering studies on Zn0.99Cu0.01O. We observed the substantial lowering of the transition pressure threshold from the wurtzite to rock salt phase compared to pristine ZnO. Experimental findings are also supported through computational data from density functional theory simulations. The charge transfer from a Cu atom in ZnO may be responsible for the reduction in the transition pressure threshold.

High pressure studies on α-cristobalite form of Al0.5Ga0.5PO4: hydrostatic versus non-hydrostatic conditions

ABSTRACTHigh pressure angle-dispersive X-ray diffraction investigations have been carried out on α-cristobalite form of Al0.5Ga0.5PO4. Our investigations show that the structural stability of this phase under high pressure depends on the nature of pressure conditions in the diamond anvil cell. Under hydrostatic pressure conditions using neon as a pressure transmitting medium, ambient orthorhombic C2221 phase transforms to orthorhombic Cmcm phase at 4.9 GPa. The high pressure Cmcm phase remains stable up to the highest pressure in the experiment, i.e. 19 GPa. The values of bulk modulus for C2221 and Cmcm phases are 19(2) and 126(4) GPa, respectively. In contrast to this, under non-hydrostatic pressure conditions, transformation of ambient C2221 phase to Cmcm phase has not observed up to 17.4 GPa. Instead, a new monoclinic phase P21 is observed which contains layers of six coordinated Al/Ga ions separated by less dense five coordinated Al/Ga ions.

Strengthening effects of interstitial nitrogen on rhenium

Introducing interstitial nitrogen atoms into the rhenium lattices is accepted for enhancing the mechanical and thermal properties of the metal. Here, we present an experimental study on the strengthening effects of interstitial nitrogen in rhenium on bulk modulus B0 and elastic shear constant C44 by comparing the difference in the compression and vibration behaviors between Re3N and Re in the in situ high pressure angle dispersive X-ray diffraction and high-pressure Raman scattering. The incorporation of interstitial N atoms introduces the covalent bonding and the special Z-type structure along the c-axis, which caused the bulk modulus B0 and elastic shear constant C44 increase by 14% and 15%, and the incompressibility of the c-axis is obviously enhanced. In addition, this work well explains the strengthening effects of interstitial N atoms on mechanical and vibrational properties.

Studies on the structural stability of Co2P2O7 under pressure

The crystal structural evolution of Co2P2O7 was studied by using in situ high pressure angle dispersive x-ray diffraction with synchrotron radiation. The results demonstrate that the α phase of Co2P2O7 goes through a partially irreversible structural transformation to β phase under pressure. The pressure is conductive to reduce the longest CoO bond length of the α phase, and then more uniform CoO bonds and regular hexagonal arrangement of CoO6 octahedra of the β phase are favored. According to the Birch-Murnaghan equation, the fitted bulk modulus B0 is 158.1(±5.6) GPa for α phase and 276.5(±6.5) GPa for β phase. Furthermore, the first-principles calculations show that these two phases of Co2P2O7 have almost equal total energies, and also have similar band structures and spin-polarized density of states at their ground states. This may be the reason why these two phases of Co2P2O7 can coexist in the pressure released state. It is found that the band gap energies decrease with increasing pressure for both phases.

Structural evolution of Lanthanide-based metallic glasses under high pressure annealing

The structural evolutions of Lanthanide-based metallic glasses under high pressure annealing were investigated by using X-ray diffraction, differential scanning calorimetry, in situ high pressure angle dispersive X-ray diffraction measurements with synchrotron radiation, and nanoindentation. The results show that the amorphous structure in the glasses keeps quite stable up to approximately 40GPa at room temperature. The high pressure annealing treatments reveal that pressure can inhibit the crystallization process, improve local packing efficiency, and restrain long-range atom diffusion. The thermal stability and hardness of the alloys both improved after the treatment. The approach has implications for the design of the microstructure- and property-controllable functional materials for various applications.

Strength and equation of state of fluorite phase CeO2 under high pressure

Fluorite phase CeO2 is compressed non-hydrostatically up to 27 GPa using a diamond anvil cell until the transition to α-PbCl2 phase occurred. The compressive strength (t) of CeO2 as a function of pressure is determined by the line width analysis of the high pressure angle dispersive x-ray diffraction patterns. The strength of CeO2 increases quickly below 3.30 GPa and reaches a plateau region at high pressures. A procedure combined the line width analysis and the line shift analysis together, based on the non-hydrostatic data to obtain the corresponding lattice parameter under hydrostatic pressures, is proposed and applied to the case of CeO2 sample. The bulk modulus and its pressure derivative of fluorite phase CeO2 (K0 = 235 (18) GPa, K0′ = 3.67) are obtained by fitting the P-V results into Vinet equation of state. A discussion of the pressure dependence of α, which determines the relative weights of the isostress and isostrain conditions across the grain boundary in an actual case, is presented.

Phase transition of cadmium fluoride under high pressure

We investigated the high pressure phases of CdF 2 by a joint theoretical and experimental study. The structural and electronic properties of CdF 2 were extensively explored to high pressure by ab initio calculations based on the density functional theory. A structural phase transition from the fluorite-type ( Fm-3m, Z = 4 ) structure to the cotunnite-type ( Pnma, Z = 4 ) structure was estimated below 8 GPa, and this phase transition was examined by the high pressure experiments up to 35 GPa at room temperature. Both high pressure angle dispersive X-ray diffraction and Raman spectroscopy experiments provided convincing evidence to verify the phase transition. Our work makes clear pressure-induced phase transitions and structural information of CdF 2 under high pressure.

Elastic and structural instability of cubicSn3N4andC3N4under pressure

We use in-situ high pressure angle dispersive x-ray diffraction measurements to determine the equation of state of cubic tin nitride Sn3N4 under pressure up to about 26 GPa. While we find no evidence for any structural phase transition, our estimate of the bulk modulus (B) is 145 GPa, much lower than the earlier theoretical estimates and that of other group IV-nitrides. We corroborate and understand these results with complementary first-principles analysis of structural, elastic and vibrational properties of group IV-nitrides, and predict a structural transition of Sn3N4 at a higher pressure of 88 GPa compared to earlier predictions of 40 GPa. Our comparative analysis of cubic nitrides shows that bulk modulus of cubic C3N4 is the highest (379 GPa) while it is structurally unstable and should not exist at ambient conditions.

In situ X-ray diffraction investigation of compression behavior in Gd40Y16Al24Co20 bulk metallic glass under high pressure with synchrotron radiation

The compression behavior of the heavy RE-based BMG Gd40Y16Al24Co20 under high pressure has been investigated by in situ high pressure angle dispersive X-ray diffraction measurements using synchrotron radiation in the pressure range of 0∼33.42 GPa at room temperature. By fitting the static equation of state at room temperature, we find the value of bulk modulus B is 61.27±4 GPa which is in good agreement with the experimental study by pulse-echo techniques of 58 GPa. The results show that the amorphous structure in the heavy RE-based BMG Gd40Y16Al24Co20 keeps quite stable up to 33.42 GPa although its compressibility is as large as about 33%. The coexistence of normal local structure similar to that of other BMGs and covalent bond structure similar to those of oxide glasses may be the reason for the anomalous property under high pressure of the Gd40Y16Al24Co20 BMG.

Investigation of the phase stability ofLuVO4 at high pressure using powder x-ray diffraction measurements and lattice dynamicalcalculations

High pressure angle dispersive x-ray diffraction measurements are carried out onLuVO4 in adiamond anvil cell up to 33 GPa at the Elettra synchrotron radiation source. The measurements showthat LuVO4 undergoes a zircon to scheelite structure phase transition with a volume change of about11% at about 8 GPa. A second transition to a monoclinic fergusonite structure occurs above16 GPa. The data are also recorded while releasing the pressure, and indicate that thescheelite phase is metastable under ambient conditions. The equations of stateand changes in internal structural parameters are reported for various phases ofLuVO4. Lattice dynamical calculations based on a transferable interatomic potential were alsoperformed and the results support the stability of the scheelite structure at high pressures.The calculated structure, equation of state and bulk modulus for all the phases are in fairagreement with the experimental observations.

High pressure X-ray diffraction and electrical resistance study of the quasi-one-dimensional sulfide InV 6S 8

The ambient structural details and the results of room temperature high pressure angle dispersive X-ray diffraction and electrical resistance measurements on the quasi-one-dimensional sulfide, InV 6S 8, to a pressure of 25 GPa are reported. The material does not undergo a phase transition in this pressure range, though an anomaly in the c/ a ratio has been observed around 10 Gpa. A fit of the Murnaghan equation of state to the V/ V 0 versus pressure data, with the value of the derivative of B 0 with respect to pressure, B′ 0, fixed at 4 has yielded a value of the bulk modulus, B 0, of 110 GPa. We also present data of the pressure dependence of the lattice constants, a and c, the ratio c/ a, and the resistance at room temperature.