In-Situ High Temperature X-Ray Diffraction Study of Structure and Phase Transformation of Nd-FePt Alloys

The structure and disorder-order transformation of NdxFe60.5-x Pt39.5（x = 0, 0.5, 1.0, 1.5） alloys were investigated in situ by high temperature X-ray diffraction. The results show that the lattice parameter a of disordered γ phase （FCC, Al structure type） and the lattice parameter ratio c/a of ordered γ1 phase （FCT, L10 structure type） increase linearly with increasing Nd concentration, whereas the c/a ratio decreases with increasing temperature. The transition temperature from ordered FCT to disordered FCC decreases with increasing Nd concentration, but for alloys quenched rapidly from γ phase region into ice-water it increases with increasing Nd.

Thermal expansivity of geikielite and ilmenite utilizing in-situ synchrotron X-ray diffraction at high temperature

The unit-cell parameters and volumes of geikielite(MgTiO_(3))and ilmenite(FeTiO_(3))were investigated at high temperatures up to 700 K and ambient pressure,using in-situ angle-dispersive synchrotron X-ray diffraction.No phase transition was detected over the experimental temperature range.Using(Berman in J Petrol29:445-522,1988.10.1093/petrology/29.2.445)equations to fit the temperature-volume data,the volumetric thermal expansion coefficients at ambient conditions(α_(V0))of MgTiO_(3) and FeTiO_(3) were obtained as follows:2.55(6)×10^(-5)K^(-1)and 2.82(10)×10^(-5)K^(-1),respectively.We infer that the larger effective ionic radius of Fe^(2+)(Ⅵ)(0.78 A)than that of Mg^(2+)(Ⅵ)(0.72?)renders FeTiO_(3)has a larger volumetric thermal expansivity than MgTiO_(3).Simultaneously,the refined axial thermal expansion coefficients under ambient conditions areα_(a0)=0.74(3)×10^(-5)K^(-1)andα_(c0)=1.08(5)×10^(-5)K^(-1)for the aaxis and c-axis of MgTiO_(3),respectively,andα_(a0)=0.95(5)×10^(-5)K^(-1)andα_(c0)=0.92(12)×10^(-5)K^(-1)for the aaxis and c-axis of FeTiO_(3),respectively.The axial thermal expansivity of MgTiO_(3) is anisotropic,but that of FeTiO_(3) is nearly isotropic.We infer that the main reason for the different axial thermal expansivity between MgTiO_(3) and FeTiO_(3) is that the thermal expansion mode of the Mg-O bond in MgTiO_(3) is different from that of the Fe-O bonds in FeTiO_(3).

Temperature-dependent constitutive modeling of a magnesium alloy ZEK100 sheet using crystal plasticity models combined with in situ high-energy X-ray diffraction experiment

A multiscale crystal plasticity model accounting for temperature-dependent mechanical behaviors without introducing a larger number of unknown parameters was developed.The model was implemented in elastic-plastic self-consistent(EPSC)and crystal plasticity finite element(CPFE)frameworks for grain-scale simulations.A computationally efficient EPSC model was first employed to estimate the critical resolved shear stress and hardening parameters of the slip and twin systems available in a hexagonal close-packed magnesium alloy,ZEK100.The constitutive parameters were thereafter refined using the CPFE.The crystal plasticity frameworks incorporated with the temperature-dependent constitutive model were used to predict stress–strain curves in macroscale and lattice strains in microscale at different testing temperatures up to 200℃.In particular,the predictions by the crystal plasticity models were compared with the measured lattice strain data at the elevated temperatures by in situ high-energy X-ray diffraction,for the first time.The comparison in the multiscale improved the fidelity of the developed temperature-dependent constitutive model and validated the assumption with regard to the temperature dependency of available slip and twin systems in the magnesium alloy.Finally,this work provides a time-efficient and precise modeling scheme for magnesium alloys at elevated temperatures.

X-Ray Diffraction Studies of Rice Husk Ash—An Ecofriendly Concrete at Different Temperatures

In the majority of rice producing countries, much of the husk produced from the processing of rice is either burnt or dumped as waste. Rice husks are one of the largest readily available but most under-utilized biomass resources, being an ideal fuel for electricity generation. In this communication the author reported the X-ray diffraction studies on rice husk ash (RHA) concrete samples heated at 300℃ and 1000℃ which were compared and observed that at 300℃ the inner surface of the specimen shows an extra compound. Copper Iron Lead Telluride Cu3FePbTe4 along with SiO2, Al5Fe2ZnO4 was present on the surface which also and might be responsible for imparting additional strength to 7.5% RHA concrete at 300℃. The X-ray diffraction studies of samples exposed to 1000℃ on temperature showed that the additional chemical compounds formed at lower temperatures were not found at 1000℃ at outer and inner surfaces of the sample indicating its possible reason for exhibiting poor strengths for all specimens. The outer surface of the 1000℃ heated specimen showed a compound named dichloroglyoxime C2H2Cl2N2O2 along with SiO2 but the inner surface of the same sample showed SiO2 alone.

High pressure x-ray diffraction techniques with synchrotron radiation

This article summarizes the developments of experimental techniques for high pressure x-ray diffraction（XRD） in diamond anvil cells（DACs） using synchrotron radiation. Basic principles and experimental methods for various diffraction geometry are described, including powder diffraction, single crystal diffraction, radial diffraction, as well as coupling with laser heating system. Resolution in d-spacing of different diffraction modes is discussed. More recent progress, such as extended application of single crystal diffraction for measurements of multigrain and electron density distribution, timeresolved diffraction with dynamic DAC and development of modulated heating techniques are briefly introduced. The current status of the high pressure beamline at BSRF（Beijing Synchrotron Radiation Facility） and some results are also presented.

An in situ high-pressure X-ray diffraction experiment on hydroxyapophyllite

The compression behavior of a natural hydroxyapophyllite is investigated up to about 10.01 GPa at 300 K using in situ angle-dispersive X-ray diffraction and a diamond anvil cell at the High Pressure Experiment Station, Beijing Synchrotron Radiation Facility （BSRF）. Over this pressure range, no phase change or disproportionation is observed. The isothermal equation of state is determined for the first time. The values of zero-pressure volume V0, isothermal bulk modulus K0, and K0＇ refined with a third-order Birch-Mumaghan equation of state are V0 = 1276.3 ± 0.9 A3, K0 = 71± 3 GPa, and K0＇ = 8 ±1. Furthermore, we confirm that the values of linear compressibility β along the a and c directions of hydroxyapophyllite are elastically anisotropic.

High-pressure effect on inverse spinel LiCuVO_4:X-ray diffraction and Raman scattering

The effect of external quasi-hydrostatic pressure on the inverse spinel structure of LiCuVO4 was studied in this paper. High-pressure synchrotron X-ray diffraction and Raman spectroscopy measurements were carried out at room temperature up to 35.7 and 40.3 GPa, respectively. At a pressure of about 20 GPa, both Raman spectra and X-ray diffraction results indicate that LiCuVO4 was transformed into a monoclinic phase, which remained stable up to at least 35.7 GPa. Upon release of pressure, the high-pressure phase returned to the initial phase. The pressure dependence of the volume of low pressure orthorhombic phase and high-pressure monoclinic phase were described by a second-order Birch-Murnaghan equation of state, which yielded bulk modulus values of B0 = 197 （5） and 232（8） GPa, respectively. The results support the empirical suggestion that the oxide spinels have similar bulk modulus around 200 GPa.

Synchrotron X-Ray Diffraction Studies on the New Generation Ferromagnetic Semiconductor Li(Zn,Mn)As under High Pressure

The pressure effect on the crystalline structure of the I-II- V semiconductor Li（Zn,Mn）As ferromagnet is studied using in situ high-pressure x-ray diffraction and diamond anvil cell techniques. A phase transition starting at -11.6GPa is found. The space group of the high-pressure new phase is proposed as Pmca. Fitting with the Birch-Murnaghan equation of state, the bulk modulus B0 and its pressure derivative B0 of the ambient pressure structure with space group of F43m are B0 = 75.4 GPa and B0 = 4.3, respectively.

High-pressure investigations on Piplia Kalan eucrite meteorite using in-situ X-ray diffraction and ^(57)Fe Mssbauer spectroscopic technique up to 16 GPa

We report here high-pressure investigations on Piplia Kalan eucrite-a member of HED （Howardite -Eucrite-Diogenite） family from asteroid 4-Vesta based on synchrotron X-ray diffraction （up to 16 GPa） and ^57Fe Mossbauer spectroscopy （up to 8 GPa）. Dominant with anorthite-rich plagioclase, pigeonite-rich pyroxene and clino-ferrosilite, the sample displayed various phase transitions attaining amorphous character at 16 GPa. These phase transitions of individual components could be explained simultaneously through variations in high-pressure XRD patterns and the Mossbauer parameters. Most prominent P21/c to C2/c transition of pigeonite and ferrosilite was exhibited both as sudden variation in Mossbauer parameters and population inversion of Fe^2＋ in M1 and M2 sites between 2.9 and 3.8 GPa and variation in intensity profile in XRD patterns at 3.56 GPa. Anorthite seemed to respond more to such impact than other components in the sample. Complete amorphization in anorthite which occurred at lower pressure of - 12 GPa implied residual stress experienced due to shock impact. The presence of high pressure （monoclinic） phase of pigeonite and ferrosilite at ambient condition in this eucrite sample confirmed earlier suggestions of an early shock event. This report is an attempt to emphasize the role of anorthite in the determination of the residual stress due to impact process in the parent body thus to understand the behavioral differences amongst HED members.

X-ray diffraction investigation of amorphous calcium phosphate and hydroxyapatite under ultra-high hydrostatic pressure

The changes in the crystal structures of synthetically prepared amorphous calcium phosphate（ACP） and hydroxyapatite（HAP） in water（1：1 mass ratio） were studied by synchrotron X-ray diffraction（XRD） under ultra-high hydrostatic pressures as high as 2.34 GPa for ACP and 4 GPa for HAP. At ambient pressure, the XRD patterns of the ACP and HAP samples in capillary tubes and their environmental scanning electron micrographs indicated amorphous and crystalline characteristics for ACP and HAP, respectively. At pressures greater than 0.25 GPa, an additional broad peak was observed in the XRD pattern of the ACP phase, indicating a partial phase transition from an amorphous phase to a new high-pressure amorphous phase. The peak areas and positions of the ACP phase, as obtained through fitting of the experimental data, indicated that the ACP exhibited increased pseudo-crystalline behavior at pressures greater than 0.96 GPa. Conversely, no structural changes were observed for the HAP phase up to the highest applied pressure of 4 GPa. For HAP, a unit-cell reduction during compression was evidenced by a reduction in both refined lattice parameters a and c. Both ACP and HAP reverted to their original structures when the pressure was fully released to ambient pressure.

Neutron powder diffraction and high-pressure synchrotron x-ray diffraction study of tantalum nitrides

Tantalum nitride （TAN） compact with a Vickers hardness of 26 GPa is prepared by a high-pressure and high- temperature （HPHT） method. The crystal structure and atom occupations of WC-type TaN have been investigated by neutron powder diffraction, and the compressibility of WC-type TaN has been investigated by using in-situ high-pressure synchrotron x-ray diffraction. The third-order Birch-Murnaghan equation of state fitted to the x-ray diffraction pressure- volume （P-V） sets of data, collected up to 41 GPa, yields ambient pressure isothermal bulk moduli of B0 = 369（2） GPa with pressure derivatives of B~ = 4 for the WC-type TaN. The bulk modulus of WC-type TaN is not in good agreement with the previous result （Bo = 351 GPa）, which is close to the recent theoretical calculation result （Bo = 378 GPa）. An analysis of the experiment results shows that crystal structure of WC-type TaN can be viewed as alternate stacking of Ta and N layers along the c direction, and the covalent Ta-N bonds between Ta and N layers along the c axis in the crystal structure play an important role in the incompressibility and hardness of WC-type TaN.

X-ray spectra of high temperature tungsten plasma calculated with collisional radiative model

Tungsten is regarded as an important candidate of plasma facing material in international thermonuclear experimental reactor （ITER）, so the determination and modeling of spectra of tungsten plasma, especially the spectra at high temperature were intensely focused on recently. In this work, using the atomic structure code of Cowan, a collisional radiative model （CRM） based on the spin-orbit-split-arrays is developed. Based on this model, the charge state distribution of tungsten ions is determined and the soft X-ray spectra from high charged ions of tungsten at different temperatures are calculated. The results show that both the average ionization charge and line positions are well agreed with others calculations and measurements with discrepancies of less than 0.63% and 1.26%, respectively. The spectra at higher temperatures are also reported and the relationship between ion abundance and temperature is predicted in this work.

Structural characterization of Al_(0.55)Ga_(0.45)N epitaxial layer determined by high resolution x-ray diffraction and transmission electron microscopy

Structural characteristics of Alo.55 Gao.45N epilayer were investigated by high resolution x-ray diffraction（HRXRD）and transmission electron microscopy（TEM）;the epilayer was grown on GaN/sapphire substrates using a high-temperature A1 N interlayer by metal organic chemical vapor deposition technique.The mosaic characteristics including tilt,twist,heterogeneous strain,and correlation lengths were extracted by symmetric and asymmetric XRD rocking curves as well as reciprocal space map（RSM）.According to Williamson-Hall plots,the vertical coherence length of AlGaN epilayer was calculated,which is consistent with the thickness of AlGaN layer measured by cross section TEM.Besides,the lateral coherence length was determined from RSM as well.Deducing from the tilt and twist results,the screw-type and edge-type dislocation densities are 1.0×10~8 cm^（-2） and 1.8×10^（10） cm^（-2）,which agree with the results observed from TEM.

Thermal expansion of kyanite at ambient pressure:An X-ray powder diffraction study up to 1000℃

The thermal expansion coefficients of kyanite at ambient pressure have been investigated by an X-ray powder diffraction technique with temperatures up to 1000 ℃. No phase transition was observed in the experimental temperature range. Data for the unit-cell parameters and temperatures were fitted empirically resulting in the following thermal expansion coefficients： αa = 5.8（3） × 10^-5, αb = 5.8 （1）× 10^-5, αc = 5.2（1）× 10^-5, and αv = 7.4（1） × 10^-3 ℃ 1 in good agreement with a recent neutron powder diffraction study. On the other hand, the variation of the unit-cell angles α, β and γ of kyanite with increase in temperature is very complicated, and the agreement among all studies is poor. The thermal expansion data at ambient pressure reported here and the compression data at ambient temperature from the literature suggest that, for the kyanite lattice, the most and least thermally expandable directions correspond to the most and least compressible directions, respectively.

High temperature mechanical behaviour of Mg-6Zn-1Y alloy with 1 wt.% calcium addition:Reinforcing effect due to I-(Mg3Zn6Yi)and Mg6Zn3Ca2 phases

The infiuence of small calcium additions on the high-temperature mechanical behaviour in an extruded Mg-6Zn-l Y(wt.%)alloy reinforced by the I-phase has been investigated.Calcium promotes the formation of the intermetallic Mg6Zn3Ca2 phase instead of 1-phase,which results in a noticeable improvement of the yield strength and ultimate tensile strength of the alloy above 100℃.The strength of the alloys was analysed taking into account the contribution due to the grain size,the crystallographic texture and the volume fraction and nature of second phase particles.In situ synchrotron radiation diffraction experiments have been used to evaluate the load partitioning between the magnesium matrix and the second phase particles(1-and MgeZgCa?phases)in both alloys.The load transfer from the magnesium matrix towards the MgeZihCa?phase is markedly more effective than that for the I-phase over the entire temperature range,especially at 200°C,temperature at which the reinforcement effect of the I-phase is null.

HIGH TEMPERATURE MOIRE INTERFEROMETRY TECHNOLOGY

In order to investigate the survivable specimen gratings, the crossed-line300 lines/mm gratings were chemically etched directly into the surface of the specimens.In order to obtain high diffraction efficiency and to minimize the shear lag, the etcheddepth of the gratings was one fourth the wave length of coherent light. The influence ofthe uneven window on the high temperature moire interferometry was preliminarily analyzed. The quartz and inconel 718 specimens were tested up to 1200℃ and 900℃. Thecrack tip deformation singular field as well as load-induced and thermal expansion displacement fields were measured by means of high temperature moire interferometry.

Relationship between boundary misorientation angle and true strain during high temperature deformation of 7050 aluminum alloy

Tensile tests of solid solution treated 7050 aluminum alloy were conducted to different strain degrees (0.1, 0.4, 0.6 and failure) at 460 ℃ with the strain rate of 1.0×10-4-1.0×10-1s-1. The boundary misorientation angle evolution during hot deformation of the 7050 aluminum alloy was studied by EBSD technique and the fracture surfaces were observed using SEM. A linear relationship between the increase in the average boundary misorientation angle and the true strain at different strain rates is assumed when aluminum alloy is deformed at 460 ℃. The increasing rate of average boundary misorientation angle is 15.1-, 15.7- and -0.75- corresponding to the strain rate of 1.0×10-4, 1.0×10-2 and 0.1 s-1, respectively. The main softening mechanism is continuous dynamic recrystallization when the strain rates are 1.0×10-4 and 1.0×10-2 s-1, and it is dynamic recovery when strain rate is 0.1 s-1.

CT Image-based Analysis on the Defect of Polypropylene Fiber Reinforced High-Strength Concrete at High Temperatures

With the application of X-ray computed tomography（CT） technology of C80 high-strength concrete with polypropylene fiber at elevated temperatures, the microscopic damage evolution process observation and image building could be obtained, based on the statistics theory and numerical analysis of the combination of concrete internal defects extension and evolution regularity of microscopic structure. The expermental results show that the defect rate has changed at different temperatures and can determine the concrete degradation threshold temperatures. Also, data analysis can help to establish the evolution equation between the defect rate and the effect of temperature damage, and identify that the addition of polypropylene fibers in the high strength concrete at high temperature can improve cracking resistance.

X-Ray and Neutron Diffraction Studies on Thermal Parameters of Thalous Bromide

Thermal parameters of TIBr were determined using both X-ray and neutron diffraction techniques. The data was analysed by Rietveld profile refinement procedure. From the neutron diffraction data, due to weak odd-order reflections, it was not possible to determine the individual thermal parameters. TheX-ray diffraction measurements yielded BT1=0.296(5) nm2 and BBr=0.162(5) nm2. The overall isotropic value, B was 0.252(7) nm2 which is in good agreement with B=0.230(8) nm2 obtained from present neutron diffraction measurements. The present values are also in good agreement with theoretical estimates obtained from the shell models.