High-resolution Powder Diffraction Research Articles

Investigation of high-pressure planetary ices by cryo-recovery. II. High-pressure apparatus, examples and a new high-pressure phase of MgSO4·5H2O.

An apparatus is described for the compression of samples to ∼2 GPa at temperatures from 80 to 300 K, rapid chilling to 80 K whilst under load and subsequent recovery into liquid nitro-gen after the load is released. In this way, a variety of quenchable high-pressure phases of many materials may be preserved for examination outside the high-pressure sample environment, with the principal benefit being the ability to obtain high-resolution powder diffraction data for phase identification and structure solution. The use of this apparatus, in combination with a newly developed cold-loadable low-temperature stage for X-ray powder diffraction (the PheniX-FL), is illustrated using ice VI (a high-pressure polymorph of ordinary water ice that is thermodynamically stable only above ∼0.6 GPa) as an example. A second example using synthetic epsomite (MgSO4·7H2O) reveals that, at ∼1.6 GPa and 293 K, it undergoes incongruent melting to form MgSO4·5H2O plus brine, contributing to a long-standing debate on the nature of the high-pressure behaviour of this and similar highly hydrated materials. The crystal structure of this new high-pressure polymorph of MgSO4·5H2O has been determined at 85 K in space group Pna21 from the X-ray powder diffraction pattern of a sample recovered into liquid nitro-gen and is found to differ from that of the known ambient-pressure phase of MgSO4·5H2O (pentahydrite, space group ), consisting of corner-sharing MgO6-SO4 ion pairs rather than infinite corner-sharing chains.

Impact of Interstitial Ni on the Thermoelectric Properties of the Half-Heusler TiNiSn.

TiNiSn is an intensively studied half-Heusler alloy that shows great potential for waste heat recovery. Here, we report on the structures and thermoelectric properties of a series of metal-rich TiNi1+ySn compositions prepared via solid-state reactions and hot pressing. A general relation between the amount of interstitial Ni and lattice parameter is determined from neutron powder diffraction. High-resolution synchrotron X-ray powder diffraction reveals the occurrence of strain broadening upon hot pressing, which is attributed to the metastable arrangement of interstitial Ni. Hall measurements confirm that interstitial Ni causes weak n-type doping and a reduction in carrier mobility, which limits the power factor to 2.5–3 mW m−1 K−2 for these samples. The thermal conductivity was modelled within the Callaway approximation and is quantitively linked to the amount of interstitial Ni, resulting in a predicted value of 12.7 W m−1 K−1 at 323 K for stoichiometric TiNiSn. Interstitial Ni leads to a reduction of the thermal band gap and moves the peak ZT = 0.4 to lower temperatures, thus offering the possibility to engineer a broad ZT plateau. This work adds further insight into the impact of small amounts of interstitial Ni on the thermal and electrical transport of TiNiSn.

Ethylene Epoxidation Catalyzed by Ag Nanoparticles on Ag-LSX Zeolites formed by Pressure- and Temperature-Induced Auto-Reduction.

Ag+ -Exchanged LSX (Ag-LSX: Ag96 Al96 Si96 O384 ⋅n H2 O), a large pore low silica analogue (Si/Al=1.0) of faujasite, was prepared and post-synthetically modified using pressure and temperature in the presence of various pore-penetrating fluids. Using high-resolution synchrotron X-ray powder and single crystal diffraction we derive structural models of the as-prepared and post-synthetically modified Ag-LSX materials. In the as-prepared Ag-LSX model, we located 96 silver cations and 245 H2 O molecules distributed over seven and five distinctive sites, respectively. At 1.4(1) GPa pressure and 150 °C in ethanol the number of silver cations within the pores of Ag-LSX is reduced by ca. 47.4 %, whereas the number of H2 O molecules is increased by ca. 40.8 %. The formation of zero-valent silver nanoparticles deposited on Ag-LSX crystallites depends on the fluid present during pressurization. Ag-nanoparticle-Ag-zeolite hybrid materials are recovered after pressure release and shown to have different chemical reactivity when used as catalysts for ethylene epoxidation.

Structure and Phase Transformation in the Giant Magnetostriction Laves-Phase SmFe2.

As one class of the most important intermetallic compounds, the binary Laves-phase is well-known for its abundant magnetic properties. Samarium-iron alloy system SmFe2 is a prototypical Laves compound that shows strong negative magnetostriction but relatively weak magnetocrystalline anisotropy. SmFe2 has been identified as a cubic Fd3̅m structure at room temperature; however, the cubic symmetry, in principle, does not match the spontaneous magnetization along the [111]cubic direction. Here we studied the crystal structure of SmFe2 by high-resolution synchrotron X-ray powder diffraction, X-ray total scattering, and selected-area electron diffraction methods. SmFe2 is found to adopt a centrosymmetric trigonal R3̅m structure at room temperature, which transforms to an orthorhombic Imma structure at 200 K. This transition is in agreement with the changes of easy magnetization direction from [111]cubic to [110]cubic direction and is further evidenced by the inflection of thermal expansion behavior, the sharp decline of the magnetic susceptibility in the field-cooling-zero field-cooling curve, and the anomaly in the specific heat capacity measurement. The revised structure and phase transformation of SmFe2 could be useful to understand the magnetostriction and related physical properties of other RM2-type pseudocubic Laves-phase intermetallic compounds.

Crystal Structure Evolution and Notable Thermal Expansion in Hybrid Perovskites Formamidinium Tin Iodide and Formamidinium Lead Bromide.

The temperature-dependent structure evolution of the hybrid halide perovskite compounds, formamidinium tin iodide (FASnI3, FA+ = CH[NH2]2+) and formamidinium lead bromide (FAPbBr3), has been monitored using high-resolution synchrotron X-ray powder diffraction between 300 and 100 K. The data are consistent with a transition from cubic Pm3m (No. 221) to tetragonal P4/mbm (No. 127) for both materials upon cooling; this occurs for FAPbBr3 between 275 and 250 K, and for FASnI3 between 250 and 225 K. Upon further cooling, between 150 and 125 K, both materials undergo a transition to an orthorhombic Pnma (No. 62) structure. The transitions are confirmed by calorimetry and dielectric measurements. In the tetragonal regime, the coefficients of volumetric thermal expansion of FASnI3 and FAPbBr3 are among the highest recorded for any extended inorganic crystalline solid, reaching 219 ppm K-1 for FASnI3 at 225 K. Atomic displacement parameters of all atoms for both materials suggest dynamic motion is occurring in the inorganic sublattice due to the flexibility of the inorganic network and dynamic lone pair stereochemical activity on the B-site. Unusual pseudocubic behavior is displayed in the tetragonal phase of the FAPbBr3, similar to that previously observed in FAPbI3.

Neutron diffraction study on Li3PO4 solid electrolyte for lithium ion battery

The solid electrolyte, Li3PO4 has been prepared by a wet chemical reaction. The crystal structure of Li3PO4 was measured at room temperature by a high resolution powder diffraction (HRPD) at the Neutron Scattering Laboratory, National Nuclear Energy Agency (BATAN), Indonesia. Another series of neutron data at 3 K and 300 K were measured by an ECHIDNA at Australian Center for Neutron Scattering, ANSTO, Australia. Based on how neutron and X-rays interact with matter, it is also important to perform the x-ray diffraction on Li3PO4. The purpose is to understand the insight crystal structure of Li3PO4 from two different methods. Both refinement results showed that crystal structure belong to the β-Li3PO4 with orthorhombic phase P m n 21 (31), with the lattice parameters are a = 6.1168 Å, b = 5.2498 Å, c = 4.8723 Å. Fourier method employed to reveal the main difference between neutron and X-rays sources. It is clearly shown that Li atom is visible to neutron. The negative scattering length of Li (−1.90) gave a negative intensity in the neutron Fourier map. In contrast to neutron, X-Ray interacts with electron gave a positive intensity but the heavy atom P dominates the intensity due to its high number of electron. The neutron can provide more detail in the structure information. By comparing the 300 K data with data 3 K, the Li-ions diffusion can be observed from the neutron Fourier maps, and the Li-ions elongation pathway can be seen from the 3-D structure model. It can be concluded here that neutron is an indispensable tool to observe the lithium ion battery materials.

Structure Transformation and Cerium-Substituted Optical Response across the Carbonitridosilicate Solid Solution (LaδY1-δ)2Si4N6C (δ = 0-0.5).

Following an investigation proving La2Si4N6C crystallizes in a monoclinic space group, isostructural to Y2Si4N6C, the reportedly hexagonal (La0.5Y0.5)2Si4N6C was reinvestigated to examine the apparent crystal structure change across the solid solution. Initially, calculating the electronic structure and phonon density of states of (La0.5Y0.5)2Si4N6C in the P63mc space group revealed an imaginary phonon mode, which is indicative of a structural instability. Displacing the atoms along the pathway of the imaginary vibration led to a previously unreported space group for carbonitridosilicates, trigonal P31c. The assignment of the trigonal space group was subsequently confirmed by synthesizing (La0.5Y0.5)2Si4N6C using high-temperature, solid state synthesis and analyzing the crystal structure with high-resolution synchrotron X-ray powder diffraction. Preparing the solid solution, (LaδY1-δ)1.98Ce0.02Si4N6C (δ = 0-0.5), showed that the crystal structure changes from the monoclinic to the trigonal space group at δ ≈ 0.25. Finally, substituting Ce3+ in the crystal structure to investigate the optical response via steady-state luminescent and photoluminescent quantum yield measurements reveals severe luminescent quenching with increasing La3+ content, due to a combination of absorption of luminescence by the host structure and thermal quenching. These results display the virtue of combining computational and experimental techniques to solve inorganic crystal structures and assess potential phosphor hosts.

Designing pseudocubic perovskites with enhanced nanoscale polarization

A crystal-chemical framework has been proposed for the design of pseudocubic perovskites with nanoscale ferroelectric order, and its applicability has been demonstrated using a series of representative solid solutions that combined ferroelectric (K0.5Bi0.5TiO3, BaTiO3, and PbTiO3) and antiferroelectric (Nd-substituted BiFeO3) end members. The pseudocubic structures obtained in these systems exhibited distortions that were coherent on a scale ranging from sub-nanometer to tens of nanometers, but, in all cases, the macroscopic distortion remained unresolvable even if using high-resolution X-ray powder diffraction. Different coherence lengths for the local atomic displacements account for the distinctly different dielectric, ferroelectric, and electromechanical properties exhibited by the samples. The guidelines identified provide a rationale for chemically tuning the coherence length to obtain the desired functional response.

Dehydration mechanism of AlPO4-5: A high-resolution synchrotron X-ray powder diffraction study

We present the results of a study on the thermal stability and dehydration dynamics of the porous aluminophosphate AlPO4-5, from room temperature to 850 °C, carried out by in situ synchrotron X-ray powder diffraction experiments. No phase transitions were observed in the investigated T range. Due to the very low interactions among framework and water molecules, dehydration is already complete at 152 °C. It occurs in two main T ranges, one between 60 and 80 °C and the second one between 90 and 120 °C. During these two stages, the cell volume tends to increase to facilitate the water release. Overall, across the full explored T range, the cell volume increase is only 0.84%, indicating that AlPO4-5 is one of the most rigid zeolite frameworks studied to date. Specifically, after complete dehydration at 200 °C, AlPO4-5 undergoes a negative thermal expansion as a consequence of the decrease in both a and c cell parameters. The expansion coefficients for V, a and c cell parameters, in the 152–850 °C range, are αV = −7.12 (10−6/K), αa = −2.5 (10−6/K), αc = −2.2 (10−6/K), respectively.

In-Situ and Real-time Monitoring of Mechanochemical Preparation of Li2 Mg(NH2 BH3 )4 and Na2 Mg(NH2 BH3 )4 and Their Thermal Dehydrogenation.

For the first time, in situ monitoring of uninterrupted mechanochemical synthesis of two bimetallic amidoboranes, M2 Mg(NH2 BH3 )4 (M=Li, Na), by means of Raman spectroscopy, has been applied. This approach allowed real-time observation of key intermediate phases, and a straightforward follow-up of the reaction course. Detailed analysis of time-dependent spectra revealed a two-step mechanism through MNH2 BH3 ⋅NH3 BH3 adducts as key intermediate phases which further reacted with MgH2 , giving M2 Mg(NH2 BH3 )4 as final products. The intermediates partially take a competitive pathway toward the oligomeric M(BH3 NH2 BH2 NH2 BH3 ) phases. The crystal structure of the novel bimetallic amidoborane Li2 Mg(NH2 BH3 )4 was solved from high-resolution powder diffraction data and showed an analogous metal coordination to Na2 Mg(NH2 BH3 )4 , but a significantly different crystal packing. Li2 Mg(NH2 BH3 )4 thermally dehydrogenates releasing highly pure H2 in the amount of 7 wt.%, and at a lower temperature then its sodium analogue, making it significantly more viable for practical applications.

Rational Design of a Commensurate (3 + 3)-D Modulated Structure within the Fast-Ion Conducting Stabilized δ-Bi2O3 Series

We report the systematic design, preparation, and characterization of the first commensurate member of the oxide-ionic conducting, (3 + 3)-D modulated, Type II phases of doped δ-Bi2O3. The incommensurate Type II modulation vector e was previously described as continuously variable, but high-resolution synchrotron X-ray powder diffraction data show that close to the composition Bi23CrNb3O45, it “locks in” to e = 1/3. The space group of the resulting 3 × 3 × 3 fluorite-type supercell was found to be F43m by selected-area electron diffraction, and the structure was solved and Rietveld-refined against neutron powder diffraction data in conjunction with local structural information from X-ray absorption spectroscopy, high-resolution transmission electron microscopy, and ab initio geometry optimization calculations. The result unambiguously validates the crystal-chemical model of the Type II phases as being based on the local ordering of oxygen around transition metals M into tetrahedral clusters of MO6 octahe...

Effect of the synthesis conditions on the properties of La0.15Sm0.35Sr0.08Ba0.42FeO3 − δ cathode material for SOFCs

The perovskite La0.15Sm0.35Sr0.08Ba0.42FeO3−δ has been prepared by the glycine nitrate (GNC) route, varying the fuel/oxidizer ratio (glycine/nitrate, G/N=1 and 2) and cooling rate (slow cooling and air-quenched), in order to study the influence of sample preparation on the materials' properties, in the context of their application as a cathode material for SOFCs. For this, the performance of the prepared mixed ion and electron conducting perovskite oxides is dictated by their structure, oxygen stoichiometry (3−δ), chemical composition and thermal expansion properties. High-resolution Synchrotron X-ray powder diffraction patterns were collected at room temperature and at 700 and 800°C. It was found that the materials had a cubic crystal structure at these temperatures. As expected, 3−δ decreased as temperature increased, and was slightly smaller for the quenched sample. Higher electrical conductivity values were obtained for the sample with G/N=1 (air-quenched) in the cooling rate. At 700 and 800°C the cathode synthesized with G/N=1 and air-quenched showed the smallest polarization resistance values in impedance spectroscopy studies. Therefore, the physicochemical and electrochemical characterization clearly demonstrated the influence of the synthetic conditions on the cathode performance.

Detailed Investigation of Anionic Redox Chemistry in Li-Rich Li2Ir0.75Sn0.5O3 Electrode Materials for Li-Ion Batteries

Li-rich layered oxides, xLi2MnO3∙(1-x)LiMO2 (M = Ni, Co, Mn) have attracted significant attention as cathode materials for lithium ion batteries in recent years. Although they exhibit promising capacities, up to 300mAh/g, due to transition metal redox reactions and unconventional oxygen redox reaction, they have several critical problems: (1) large irreversible capacity loss in the first cycle due to the release of oxygen and lithium from the lattice at the end of first charge, (2) insufficient cycling performance, (3) side reactions with electrolyte at high cut-off voltage and, (4) phase transformation that leads to voltage decay during cycling [1]. In order to improve the structural stability and investigate single redox cation, Li2M1-xSnxO3 (M = Ru, Ir) type Li-rich materials have been recently designed by taking advantage of 4d, 5d transition metals that can increase the M-O covalency. These materials are structurally related to the 3d transition metal-based traditional Li-rich cathode materials. Increased M-O bond covalency results in lower voltage plateau compared to 3d transition metal based Li-rich cathode materials and thus enables the investigation of intrinsic redox chemistry by avoiding the side reactions with electrolytes at higher voltage. In these cathode materials electrochemical process is described as ‘a cumulative and reversible cationic (Mn+ → M(n+1)+) and anionic (O2- → O2 2-) redox process, due to the d-sp hybridization associated with a reductive coupling mechanism’. This mechanism is derived by using the X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) techniques [2,3]. However, the structural changes in Li-rich layered materials during anionic redox chemistry are very complex and still remain a controversial issue that needs further investigation. In order to understand the origin of high capacity of Li-rich cathode materials, systematic investigation is required to understand the structural changes in the bulk materials during electrochemical cycling. In this study, we synthesized Li2Ir0.75Sn0.25O3 electrode material that delivered first cycle charge and discharge capacity of 214mAh/g (corresponds to removal of ~2 moles of Li+) and 188mAh/g, respectively and after 100 cycles, it was still able to deliver 128mAh/g of discharge capacity with 71% capacity retention. We performed synchrotron radiation-based high-resolution X-ray powder diffraction (HRPD) and hard & soft X-ray absorption spectroscopy (XAS) along with several electrochemical characterization techniques, to investigate the redox reaction in Li2Ir0.75Sn0.25O3 electrode in terms of local and bulk crystal structural changes, variations in the oxidation states of transition metal and oxygen ions in Li2Ir0.75Sn0.25O3, respectively. Sn K-edge XANES spectra do not show any edge shift implying that Sn-ions are not participating in the electrochemical reaction. However, we found that there is minimal contribution from Ir-ions in the charge compensation, as inferred by small changes in the Ir L3-edge XANES edge position. So the charge is mostly compensated by anionic redox chemistry mainly involving oxygen. O K-edge soft XAS spectra were measured to quantify the charge compensation by oxygen and metals. However, anionic redox chemistry is very complex as it involves significant structural changes. Understanding these structural changes during lithium extraction and insertion is a key to investigate the charge compensation mechanism of 4d and 5d metals-based Li-rich cathode materials. Rietveld refinement and profile refinement by FAULTS [4] were performed on the measured HRPD pattern to understand the detailed crystal structure variations and formation of stacking faults during charge and discharge. Detailed findings will be presented at the time of the meeting. [1] J. Wang et al. Advanced Energy Materials6 (2016) 1600906 [2] M. Sathiya et al. Nature Materials12 (2013) 827–835 [3] E. McCalla et al. Science350 (2015) 1516–1521 [4] M. Casas-Cabanas et al. Journal of Applied Crystallography49 (2016) 2259-2269

Structural and functional characterisation of KNNS–BNKZ lead-free piezoceramics

ABSTRACTPromising piezoelectric properties have been reported recently for lead-free 0.96(K0.48Na0.52Nb0.95Sb0.05)–0.04Bi0.5(Na0.82K0.18)0.5ZrO3 (KNNS–BNKZ) ceramics. The presence of coexisting rhombohedral and tetragonal phases is thought to play a key role in their functional properties, but a thorough understanding is currently lacking. In this experiment, (1−x)KNNS–(x)BNKZ ceramics with x = 0–0.05 were prepared by the mixed-oxide method. High-resolution synchrotron X-ray powder diffraction (SXPD) measurements reveal that the addition of BNKZ into KNNS ceramics leads to an increase in the rhombohedral–orthorhombic phase transition temperature (TR−O) and a decrease in the orthorhombic–tetragonal phase transition temperature (TO−T) leading to orthorhombic–tetragonal and rhombohedral–tetragonal phase coexistence at room temperature for compositions with x = 0.02 and 0.04, respectively. By combining the SXPD results with microstructure, evidence is also found for the occurrence of chemical heterogeneity, which could provide an additional means to control the functional properties. The structural observations are correlated with changes in the dielectric and ferroelectric properties.

Phase identification and structure investigation of novel quaternary rare-earth substituted titanates

Novel quaternary lanthanide-substituted oxides of stoichiometry LnxY2−xTi2O7 (where Ln is lanthanum, neodymium, samarium, gadolinium, or ytterbium) were prepared by traditional high-temperature, solid-state techniques and characterized by X-ray powder diffraction. Samples with nominal values of x up to 1.0 were attempted. The well-studied ternary cubic pyrochlore compound yttrium titanium oxide (Y2Ti2O7, space group Fd-3m, Z = 8), served as a parent structural framework in which Ln3+ cations were substituted on the Y3+ site. Laboratory-grade X-ray powder diffraction data revealed pure quaternary pyrochlore phases for LnxY2−xTi2O7 with x ≤ 0.2. Pyrochlore phase purity was verified by Rietveld analysis using high-resolution synchrotron X-ray powder diffraction data when x ≤ 0.2, however, for La3+ substitution specifically, pure quaternary pyrochlore formed at x<0.1. Band gap energies on selected samples were determined using optical diffuse reflectance spectroscopy and showed that these materials can be classified as electrical insulators with indirect band gap energies around 3.7eV.

Catalyst Shelf Life: Its Effect on Nitrogen-Doped Carbon Nanotubes

In this work is presented a study of the shelf life of an iron-impregnated MgO (Fe/MgO) sample and an explanation of the effect of its aging on morphology and electroactivity of nitrogen-doped carbon nanostructures prepared by using this catalyst at different ages. Characterizations of Fe/MgO by thermogravimetric analysis (TGA), temperature-programmed desorption mass spectroscopy (TPD-MS), high-resolution X-ray powder diffraction (HR-XRPD), and X-ray photoelectron spectroscopy (XPS) have been performed at different aging times. The catalyst is formed by crystalline MgO, Mg(OH)2, and FeO phases. During aging, CO2 adsorption induces the formation of amorphous carbonate, resulting in a decrease of specific surface area, a redistribution of porosity, a reduction of the iron percentage at the surface, and an increase of iron oxide particle size. Different surface and bulk properties are used to explain different morphologies and electroactivities of the nitrogen-doped carbon nanotubes synthesized at different ...

Anomalous Thermal Expansion of HoCo0.5Cr0.5O3 Probed by X-ray Synchrotron Powder Diffraction

Mixed holmium cobaltite-chromite HoCo0.5Cr0.5O3 with orthorhombic perovskite structure (structure type GdFeO3, space group Pbnm) was obtained by solid state reaction of corresponding oxides in air at 1373 K. Room- and high-temperature structural parameters were derived from high-resolution X-ray synchrotron powder diffraction data collected in situ in the temperature range of 300–1140 K. Analysis of the results obtained revealed anomalous thermal expansion of HoCo0.5Cr0.5O3, which is reflected in a sigmoidal temperature dependence of the unit cell parameters and in abnormal increase of the thermal expansion coefficients with a broad maxima near 900 K. Pronounced anomalies are also observed for interatomic distances and angles within Co/CrO6 octahedra, tilt angles of octahedra and atomic displacement parameters. The observed anomalies are associated with the changes of spin state of Co3+ ions and insulator-metal transition occurring in HoCo0.5Cr0.5O3.

Possibility to realize spin-orbit-induced correlated physics in iridium fluorides

Recent theoretical predictions of "unprecedented proximity" of the electronic ground state of iridium fluorides to the SU(2) symmetric $j_{\mathrm{eff}}=1/2$ limit, relevant for superconductivity in iridates, motivated us to investigate their crystal and electronic structure. To this aim, we performed high-resolution x-ray powder diffraction, Ir L$_3$-edge resonant inelastic x-ray scattering, and quantum chemical calculations on Rb$_2$[IrF$_6$] and other iridium fluorides. Our results are consistent with the Mott insulating scenario predicted by Birol and Haule [Phys. Rev. Lett. 114, 096403 (2015)], but we observe a sizable deviation of the $j_{\mathrm{eff}}=1/2$ state from the SU(2) symmetric limit. Interactions beyond the first coordination shell of iridium are negligible, hence the iridium fluorides do not show any magnetic ordering down to at least 20 K. A larger spin-orbit coupling in iridium fluorides compared to oxides is ascribed to a reduction of the degree of covalency, with consequences on the possibility to realize spin-orbit-induced strongly correlated physics in iridium fluorides.

Physical and Magnetic Properties of La0.5Ca0.5Mn0.9Cu0.1O3 at Temperature in the Range of 10-100 K

We have successfully measured physical and magnetic properties of the La0.5Ca0.5Mn0.9Cu0.1O3 at temperature in the range of 10-100 K. Physical properties have covered electrical resistivity and specific heat. The properties, which serve as a function of temperature, were investigated by using Physics Properties Measurement System (PPMS) with and without an external magnetic field up to 8.5 Tesla. The magnetic structure was characterized using High-Resolution Powder Diffraction (HRPD) at room and low temperatures. Furthermore, the magnetization was measured by using Magnetic Properties Measurement System (MPMS) with the external magnetic field of 0-7 Tesla. In the temperature interval of 10-53 K, the resistivity of the sample increased with the increasing of external magnetic field. At temperatures T < 53 K, the samples were crystalline metal. This was revealed by fitting the graph Ln R as a function of 1/T. At temperatures T > 53 K, the sample was an insulator according to fittings Ln R as a function of 1/T0.25. The result was also shown by the decreasing value of the resistivity of the sample. The transition temperature of the metal-insulator (TMI) decreased with the increasing of external magnetic field, i.e. from 60 K without an external magnetic field to 53 K with external magnetic field 8.5 Tesla. A coefficient electron specific heat and specific heat of spin wave increased, and phonon specific heat was relatively unchanged in the presence of an external magnetic field. Results of HRPD experiment were analyzed by using Fullprof program. At room temperature, the sample had the paramagnetic phase, while at low temperatures of 20 K it had antiferromagnetic phase. Temperature phase transition from the paramagnetic to antiferromagnetic phase or Neel temperature was around 225 K. However, the saturation magnetization of the sample was not observed.

The new structure transition sequences of cerium around 5 GPa

A fascinating structure transition of cerium around 5 GPa has been studied using high-resolution synchrotron angle-dispersive powder diffraction techniques. This study indicates that the structural transition of cerium strongly depends on the process of compression. Two runs experiments with different compression conditions demonstrate two different structural transition sequences at room temperature around 5 GPa, fcc′→C2/m →bct for regular compression, fcc′→C2/m →α-U→bct for the pre-compression. These results show that pressure is not the only factor to determining structural transformation at high pressure, and the structural transformation sequences can be varied by changing the external conditions e.g. pre-compression.