Angle Dispersive X-ray Diffraction Studies Research Articles

An experimental investigation on the combined effect of plastic deformation and grain size variation on the acoustic nonlinearity parameter.

The combined effect of grain size variation and plastic deformation on the acoustic nonlinearity parameter has been investigated in an austenitic stainless-steel material of grade 304. The nonlinear behavior of this parameter with grain growth has deviated to linear fit with deformation. This is due to the interaction of elastic waves with the strain-induced dislocation substructure in the grains. The normalized mean square strain of the deformed specimens has been estimated through angle dispersive x-ray diffraction studies using a synchrotron source, and this has been correlated with the change in the acoustic non-linearity parameter with deformation. The nonlinearity parameter is found to be very sensitive to the plastic deformation even in the presence of grain size variations. The results infer that the variations in the nonlinearity parameter can be used to have an estimate of the extent of localized deformations often occurring during the fabrication of metallic components.

High-pressure angle-dispersive X-ray diffraction study of mechanically alloyed SnSe2

The effect of pressure on mechanically alloyed trigonal nanostructured SnSe2 (n-SnSe2) was studied by in situ angle-dispersive X-ray diffraction up to 25.8 GPa. The pressure dependence of lattice parameters and unit cell volume was investigated. By fitting the lattice parameters and unit cell volume to a third-order Birch–Murnaghan equation of state for several values of the applied pressure, the bulk modulus B0, its first derivative B′, and the linear moduli along the a- and c-axes were determined. The effect of pressure on the z coordinate of site 2d occupied by Se atoms was investigated using pair distribution function analysis. The results were compared with experimental and theoretical studies of SnS2 and SnSe2 reported in the literature.

Magnetic and Structural Phase Transitions in Thulium under High Pressures and Low Temperatures

The nature of 4f electrons in many rare earth metals and compounds may be broadly characterized as being either “localized” or “itinerant”, and is held responsible for a wide range of physical and chemical properties. The pressure variable has a very dramatic effect on the electronic structure of rare earth metals which in turn drives a sequence of structural and magnetic transitions. We have carried out four-probe electrical resistance measurements on rare earth metal Thulium (Tm) under high pressures to 33 GPa and low temperatures to 10 K to monitor the magnetic ordering transition. These studies are complemented by angle dispersive x-ray diffraction studies to monitor crystallographic phase transitions at high pressures and low temperatures. We observe an abrupt increase in magnetic ordering temperature in Tm at a pressure of 17 GPa on phase transition from ambient pressure hcp-phase to α-Sm phase transition. In addition, measured equation of state (EOS) at low temperatures show anomalously low thermal expansion coefficients likely linked to magnetic transitions.

High pressure phase transitions in scheelite structured fluoride: ErLiF4

Our synchrotron based angle dispersive x-ray diffraction studies on scheelite structured ErLiF4 show that it undergoes two phase transitions, at ~11.5 and ~15.5GPa to lower symmetry monoclinic phases, before becoming (irreversibly) amorphous at ~28GPa. The first high pressure phase transformation to the fergusonite structure (space group I2/a) is found to be of thermodynamically second order. The second high pressure phase could be fitted to the P2/c space group, but detailed analysis rules out the wolframite structure (P2/c space group), common to many scheelite compounds under high pressures. We also suggest that despite the ionic character of the LiF4 tetrahedra, the compressibility of LnLiF4 (Ln=Eu–Lu) kind of scheelites is more affected by the LnF8 dodecahedra than the LiF4 tetrahedra.

High-pressure behavior and thermoelastic properties of niobium studied by in situ x-ray diffraction

In situ synchrotron energy dispersive x-ray diffraction (XRD) experiments on Nb have been conducted at pressures up to 6.4 GPa and temperatures up to 1073 K. From the pressure-volume-temperature measurements, thermoelastic parameters were derived for the first time for Nb based on the thermal pressure (ΔPth) equation of state (EOS), modified high-T Birch-Murnaghan EOS, and Mie-Grüneisen-Debye EOS. With the pressure derivative of the bulk modulus KT′ fixed at 4.0, we obtained the ambient isothermal bulk modulus KT0 = 174(5) GPa, the temperature derivative of bulk modulus at constant pressure (∂KT/∂T)P=−0.060(8) GPa K−1 and at constant volume (∂KT/∂T)V=−0.046(8) GPa K−1, the volumetric thermal expansivity αT(T)=2.3(3)×10−5+0.3(2)×10−8T (K−1), as well as the pressure dependence of thermal expansion (∂α/∂P)T=(−2.0±0.4)×10−6 K−1 GPa−1. Fitting the present data to the Mie-Grüneisen-Debye EOS with Debye temperature Θ0 = 276.6 K gives γ0 = 1.27(8) and KT0 = 171(3) GPa at a fixed value of q = 3.0. The ambient isothermal bulk modulus and Grüneisen parameter derived from this work are comparable to previously reported values from both experimental and theoretical studies. An in situ high-resolution, angle dispersive XRD study on Nb did not indicate any anomalous behavior related to pressure-induced electronic topological transitions at ∼5 GPa as has been reported previously.

The novel phase transition of NaBi(WO4)2 under high pressure

The Raman and synchrotron angle-dispersive X-ray diffraction studies have been performed on NaBi(WO 4 ) 2 under high pressure up to 30.7 and 36.2 GPa, respectively, at room temperature. With pressure increases to ∼7.0 GPa, the structure of NaBi(WO 4 ) 2 begins to transform from tetragonal ( I 4 1 / a ) into monoclinic ( P 2/ m ), and the phase transition completes around 13 GPa. With pressure higher than 29.0 GPa, the NaBi(WO 4 ) 2 turns into amorphous state. The random arrangement of Na + and Bi 3+ in short-range ordered scheelite NaBi(WO 4 ) 2 results in the tetragonal to monoclinic phase transition, which is different from that observed in AWO 4 tungstates and AMoO 4 molybdates (A=Ca, Sr, Ba, Pb, Eu, Cd). The NaBi(WO 4 ) 2 transforms from tetragonal into monoclinic, which starts around 7 GPa and completes at about 13 GPa. With pressure higher than 29 GPa, the NaBi(WO 4 ) 2 turns into amorphous state. ► Raman and X-ray diffraction studies performed on NaBi(WO 4 ) 2 up to 30.7 and 36.2 GPa, respectively. ► The tetragonal ( I 4 1 / a ) into monoclinic ( P 2/ m ) phase transition is determined. ► With pressure higher than 29 GPa, the NaBi(WO 4 ) 2 ultimately turns into amorphous state. ► The ambient pressure bulk modulus and volume of tetragonal and monoclinic phases are obtained.

Effect of the surfactant CTAB on the high pressure behavior of CdS nano particles

Angle dispersive x-ray diffraction studies on CTAB capped cadmium sulphide (CdS) nano particles of sizes 70 nm, 44 nm and 10 nm have been carried out up to ∼39, ∼30 and ∼28 GPa respectively. All the three types of nano particles transform to the rocksalt phase at pressures higher than that of bulk CdS. Our analysis of the x-ray diffraction data indicates that the phase transition pressure as well as the bulk modulus of the rocksalt phase of CdS exhibits a non monotonous behaviour as a function of the size of the nano particles. Our high pressure Raman scattering studies on the 10 nm CdS nano particles are in agreement with the x-ray diffraction studies. The presence of the Raman mode in the high pressure rocksalt phase may be attributed to a disorder activated scattering in this phase or to the formation of a core shell structure beyond the transformation pressure.

Ammonia molecule rotation of pressure-induced phase transition in ammonia hemihydrates 2NH3·H2O

High-pressure Raman scattering and synchrotron angle-dispersive X-ray diffraction studies have been performed on liquid ammonia hemihydrates (2NH3·H2O) at room temperature up to 41.0 GPa. The results demonstrate that liquid 2NH3·H2O transforms into a solid phase at 3.5 GPa. Upon increasing pressure, a solid-solid phase transition is observed at about 19.0 GPa. When pressure is increased up to 25.8 GPa, another solid-solid phase transition is obtained. The first solid-solid phase transition at about 19.0 GPa originates from the rotation of type II ammonia molecule via the O–H⋯N bond, and this phase transition is from orthorhombic to body-centered-cubic. High-pressure Raman scattering and X-ray diffraction results of 2NH3·H2O provide significant information for better understanding the physical properties of the ammonia–water binary system under extreme conditions, and further for the structure state of the outer planets and large satellites in the solar system.

Pressure-induced crystallization and phase transformation of amorphous selenium: Ramanspectroscopy and x-ray diffraction studies

High-pressure Raman spectroscopy studies have been carried out on amorphous Se (a-Se)at room temperature in a diamond anvil cell with an 830 nm exciting line. Raman evidencefor the pressure-induced crystallization of a-Se and the coexistence of the unknownhigh-pressure phase with the hexagonal phase is presented for the first time. Furtherexperimental proof of high-pressure angle-dispersive x-ray diffraction studies for a-Seindicates that the unknown high-pressure phase is also a mixture phase of the tetragonalI41/acd and Se IV structure. Our Raman and x-ray diffraction results suggest that hexagonal Se Iundergoes a direct transition to triclinic Se III at about 19 GPa, which is in good agreementwith the theoretical prediction.

Equations of state of several iron–tin intermetallic compounds

Abstract An angle-dispersive X-ray diffraction study was performed on the Fe–Sn intermetallic compounds FeSn2, FeSn, and Fe3Sn to a pressure of 25 GPa using nitrogen as a pressure-transmitting medium and gold as a pressure marker. The samples were prepared with phase purities of more than 97%. These intermetallics show no phase transition to the highest pressure achieved. Our data fitted to the Birch–Murnaghan equation of state yield: K 0 = 86 ( 2 ) GPa for FeSn2, K 0 = 94 ( 2 ) GPa for FeSn, and K 0 = 122 ( 3 ) GPa for Fe3Sn. The c/a ratio increases with pressure for FeSn2 and Fe3Sn but decreases for FeSn.

The Orthorhombic Structure of Iron: An in Situ Study at High-Temperature and High-Pressure

An in situ angle-dispersive x-ray diffraction study was undertaken of iron in a laser-heated, diamond-anvil cell up to 2375 kelvin and between 30 and 100 gigapascals in Al 2 O 3 - and SiO 2 -pressure media. The resolution and reliability of diffraction peak intensities allow quantitative assessment of a structural model. The results confirm that iron undergoes a phase transformation at high pressures and temperatures. The space group is Pbcm for an orthorhombic lattice, and the atomic topology is close to that of ɛ hexagonal close-packed iron.