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A magnetic order can be completely suppressed at zero temperature (T), by doping carriers or applying pressure, at a quantum critical point, around which physical properties change drastically. However, the situation is unclear for an electronic nematic order that breaks rotation symmetry. Here, we report nuclear magnetic resonance studies on NaFe_{1-x}Co_{x}As where magnetic and nematic transitions are well separated. The nuclear magnetic resonance spectrum is sensitive to inhomogeneous magnetic fields in the vortex state, which is related to London penetration depth λ_{L} that measures the electron mass m^{*}. We discovered two peaks in the doping dependence of λ_{L}^{2}(T∼0), one at x_{M}=0.027 where the spin-lattice relaxation rate shows quantum critical behavior, and another at x_{c}=0.032 around which the nematic transition temperature extrapolates to zero and the electrical resistivity shows a T-linear variation. Our results indicate that a nematic quantum critical point lies beneath the superconducting dome at x_{c} where m^{*} is enhanced. The impact of the nematic fluctuations on superconductivity is discussed.

Pressure technique is an effective way to modify magnetic properties of diluted magnetic semiconductors (DMS). Based on single crystal, in-plane electrical transport properties of a new generation DMS (Ba

Dilute magnetic semiconductors (DMS) are nonmagnetic semiconductors doped with magnetic transition metals. The recently discovered DMS material (Ba$_{1-x}$K$_{x}$)(Zn$_{1-y}$Mn$_{y}$)$_{2}$As$_{2}$ offers a unique and versatile control of the Curie temperature, $T_{\mathrm{C}}$, by decoupling the spin (Mn$^{2+}$, $S=5/2$) and charge (K$^{+}$) doping in different crystallographic layers. In an attempt to describe from first-principles calculations the role of hole doping in stabilizing ferromagnetic order, it was recently suggested that the antiferromagnetic exchange coupling $J$ between the nearest-neighbor Mn ions would experience a nearly twofold suppression upon doping 20\% of holes by potassium substitution. At the same time, further-neighbor interactions become increasingly ferromagnetic upon doping, leading to a rapid increase of $T_{\mathrm{C}}$. Using inelastic neutron scattering, we have observed a localized magnetic excitation at about 13 meV, associated with the destruction of the nearest-neighbor Mn-Mn singlet ground state. Hole doping results in a notable broadening of this peak, evidencing significant particle-hole damping, but with only a minor change in the peak position. We argue that this unexpected result can be explained by a combined effect of superexchange and double-exchange interactions.

The aim of this study was to establish the antioxidant status and oxidative stress in adult patients with chronic idiopathic thrombocytopenic purpura (ITP). Eighty-four patients diagnosed with chronic ITP were studied. Fifty-eight age-matched healthy subjects were selected as controls. Serum nitrogen monoxide ( NO), oxidized glutathione (GSSG), malondialdehyde (MDA), total antioxidant status (TAS), total oxidant status (TOS), superoxide dismutase(SOD), hydrogen peroxide enzyme (CAT), glutathione peroxidase (GSH-Px), glutathione (GSH) were evaluated by enzyme-linked immunosorbent assay (ELISA). It was found that serum SOD, CAT, GSH-Px, GSH, TAS levels were significantly lower in patients with chronic ITP than controls (all P

Summary Introduction: Dysfunctional cellular immunity is considered to be essential to the pathophysiology of Epstein–Barr virus-related idiopathic thrombocytopenic purpura (EBV-ITP). Cytokines in peripheral blood and the gene expression of transcription factors in T lymphocytes of patients with were investigated to correlate the polarization of T helper cell type 1 (Th1)/T helper cell type 2 (Th2) with the degree of thrombocytopenia. Methods: The expression of type 1 (T-bet) and type 2 (GATA-3) in T lymphocytes was detected by semiquantitative reverse-transcription–polymerase chain reaction, and plasma cytokine levels were measured by enzyme-linked immunoassay in 35 patients and 30 control subjects. Results: Th1/Th2 [(interleukin-2 + γ-interferon)/(interleukin-10 + interleukin-13)] cytokine ratios and transcription factor (T-bet/GATA-3) mRNA ratios were significantly decreased in patients with EBV-ITP, and the Th1/Th2 ratio was directly correlated with platelet counts. Conclusion: Our findings clearly show that type 2 polarization of the autoimmune response accounts for the expression of cytokines and transcription factors in EBV-ITP.

In this paper, transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) techniques are utilized to study the as prepared superconducting samples of Sr 2 CuO 3+ δ with different nominal δ to reveal the origin of superconductivity. The 60, 68 and 75 K superconductivities observed in these samples are revealed to arise, respectively, from the Pmmm ( a = 5 2 a p , b = 2 a p and c = c p ), Cmmm ( a = c p , b = 3 2 a p and c = 4 2 a p ) and C 2/ m ( a = 5 2 a p , b = c p , c = 26 2 / 2 a p and β = 101.3°) modulated phases. These superconducting modulated phases are suggested to be formed by the ordering of apical oxygen, and each of them is associated with a distinct type of the ordering. Oxygen K absorption edge measured by EELS indicates that these modulated phases have a similar hole doping level. Our experimental results suggest that the superconductivity differences in the Sr 2 CuO 3+ δ system are mainly caused by the reordering of apical oxygen.

The single-phase 6H BaRuO{sub 3} with the hexagonal BaTiO{sub 3} structure was synthesized at 5 GPa and 1000 deg. C. Rietveld refinement of the powder X-ray data for the 6H phase resulted in the lattice parameters to be a=5.7127(1) A and c=14.0499(2) A; the average Ru-O distance and direct Ru-Ru distance in the Ru{sub 2}O{sub 9} dioctahedron being 1.992(6) and 2.5658(14) A, respectively. The electrical resistivity of the 6H BaRuO{sub 3} follows a relationship of {rho} versus T{sup 3/2} below 60.0 K, a signature deviation from the Fermi-liquid behavior. Both magnetic susceptibility and specific heat data indicate that the 6H BaRuO{sub 3} is an exchange-enhanced Pauli paramagnet due to the electron correlation effect with large Wilson ratio R{sub W} and Stoner enhancement factor. The comprehensive evolution of transport and magnetic properties from 9R across 4H to 6H BaRuO{sub 3} was discussed. - Graphical abstract: The single-phase 6H BaRuO{sub 3} was synthesized under high pressure high temperature. The electrical resistivity of 6H BaRuO{sub 3} follows a T{sup 3/2} relation below 60.0 K. Both magnetic susceptibility and specific heat data indicate that 6H BaRuO{sub 3} is an exchange-enhanced Pauli paramagnet with the large Wilson ratio and Stoner enhancement factor.

A 75 K Sr2CuO3+δ superconductor (nominal δ = 0.4), detected to be a K2NiF4-type tetragonal single phase from x-ray powder diffraction (XRD) data, was annealed in a N2 atmosphere at different temperatures, and with raising the annealing temperature, the superconducting transition temperature (Tc) is found to increase from 75 K (as-prepared), in turn, to 89 K (post-annealed at 150 °C), 95 K (post-annealed at 250 °C), and then to disappear when further increasing the annealing temperature above 250 °C. Transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) techniques are utilized to characterize both as-prepared and post-annealed samples in order to further identify the superconducting phases. TEM investigations reveal that almost all grains in the as-prepared sample exhibit modulated structures having the K2NiF4-type tetragonal structure of Sr2CuO3+δ as their basic substructure, and two types of modulated phase, i.e., Fmmm modulated phase ( and c = cp) and C 2/m modulated phase (, b = cp, and β = 101.3°), are found in the sample. With increasing annealing temperature, successive structure phase transitions starting from the C 2/m modulated phase are observed, i.e., C 2/m modulated phase Cmmm modulated phase (a = cp, and ) (annealed at 150 °C) Pmmm modulated phase ( and c = cp) (annealed at 250 °C) unmodulated orthorhombic structure (annealed at 350 °C), while no obvious changes are found for the Fmmm modulated phase up to 250 °C. The experimental results strongly suggest that the C 2/m modulated phase is responsible for Tc at 75 K, the Cmmm modulated phase for Tc at 89 K, and the Pmmm modulated phase for Tc at 95 K, while the Fmmm modulated phase is nonsuperconducting. The absence of superconductivity in the Fmmm modulated phase can be explained by the oxygen vacancies located at the Cu–O planes, based on the previous results. For the superconducting modulated phases, the oxygen vacancies can only be located in the Sr–O layers (i.e., in the apical sites) due to the requirement of oxygen vacancy-free CuO2 planes for superconductivity, and thus their formations are naturally explained by the ordering of apical oxygen vacancies. Besides a minor effect of the hole doping level, the reordering of apical oxygen in those superconducting modulated phases is revealed to be the key factor resulting in the enhancement of Tc.

Using a first-principles calculation, we investigated some possible structures of GeH4 similar to those of SiH4 investigated by Feng et al. [J. Feng, W. Grochala, T. Jaron, R. Hoffmann, A. Bergara, N.W. Aschcroft, Phys. Rev. Lett. 96 (2006) 017006] and determined their metallization pressures. It is found that GeH4 has different case with SiH4 and has lower metallization pressure. Structure T2 in germane emerges as an enthalpically competitive structure over the pressure range 55–62 GPa. The metallization pressure for GeH4 with T3 structure is about 50 GPa, which is much lower than that of 91 GPa assumed for the O3 phase of SiH4, i.e. GeH4 could be easier to be metallized than SiH4.

Dense BaTiO(3) nanoceramics with a homogeneous grain size of 30 nm were prepared at 6 GPa, 1000 degrees C using a three-step high-pressure sintering method. The microstructure of the ceramics obtained is uniform and the relative density is above 98% of the theoretical value. Similar to normal BaTiO(3) ceramics, successive phase transitions are observed in the 30 nm BaTiO(3) ceramics using variable-temperature X-ray diffraction measurements. Furthermore the 30 mn BaTiO(3) ceramics reveal ferroelectric properties after being post-annealed at low temperature in O(2) atmosphere, but the phase transition temperature from paraelectric to ferroelectric phase is 10 degrees C lower than that of a normal bulk sample. The results indicate that dense 30 nm BaTiO(3) ceramics retain ferroelectricity above room temperature. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dense nanocrystalline BaTiO3 ceramics with uniform grain sizes of 30 nm was obtained by pressure assisted sintering. The phase transitions were investigated by Raman scattering at temperatures ranging from −190 to 200 °C. With increasing temperature, similar to 3 μm BaTiO3 normal ceramics, the successive phase transitions from rhombohedral to orthorhombic, orthorhombic to tetragonal, tetragonal to cubic were also observed in 30 nm BaTiO3 ceramics. Especially, the coexistence of ferroelectric tetragonal and orthorhombic phases was found at room temperature. The ferroelectric behavior was further characterized by P–E hysteresis loop. The experimental results indicate that the critical grain size of the disappearance of ferroelectricity in nanocrystalline BaTiO3 ceramics fabricated by pressure assisted sintering is below 30 nm.

Using the polymer-network gel method to control the chemical procedure, Sr2FeMoO6 powders with grain size of 50 nm (A) and 100 nm (B) have been synthesized, and their structural and electrical properties have been investigated. By comparing the experimental results of samples A and B with that of bulk sample C with grain size in μm obtained before, sample A shows the largest bulk modulus B 0 and a relatively large slope of the drop in resistance as a function of pressure. The possible reasons are given and discussed.

A single-phase superconductor Sr2CuO3+δ with nominal δ = 0.4 (detected from x-ray powder diffraction (XRD) data) (Tc = 75 K) has been synthesized using a high-pressure technique. The structure and microstructure of this material have been carefully studied by means of transmission electron diffraction (ED), high-resolution transmission electron microscopy (HRTEM), electron energy-loss spectroscopy (EELS) and energy dispersive analysis of x-ray (EDX) techniques. Interestingly enough, ED and HRTEM investigations reveal that almost all grains of the tetragonal form Sr2CuO3+δ exhibit modulated features. This result strongly suggests that the superconductivity at 75 K in the material is associated with the modulated phases. Two types of modulated phases having different primitive cells but equal in volume are found in the sample. One is the face-centred orthorhombic modulated phase with a space group Fmmm and lattice constants of . The other is the base-centred monoclinic modulated phase with a space group C 2/m and unit-cell parameters of , bm = cp, and β = 101.3°. The relative ratio of the former to the latter phase contents is about 4:1. Oxygen K absorption edges from EELS measurements suggest that the two modulated phases have the same hole intensity. Defects such as twin boundaries, small-angle asymmetrical tilt boundaries and dislocations are frequently observed in the C 2/m monoclinic modulated phase, and some of them are carefully studied by means of HRTEM, EELS and EDX.

A black-brown powder was synthesized from melamine (C3N6H6) at 850 degrees C and 4.5 GPa. There are two possibilities for the sample phase components based on the analyses of C/N/H elements and X-ray diffraction patterns. One is that the powder is composed of 2H-type g-C3N4 and some intermediate phases, while the other is that it consists of some undecomposed raw material, graphite and intermediate phases. The existence of the intermediate phase with long periodicity along one direction is confirmed through transmission electron microscopy observations. Scanning electron microscopy images show many block regions, in which a few holes exist. The atomic fraction of carbon and nitrogen was checked with energy dispersive X-ray analysis, and the chemical bond states were investigated by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Based on the general analysis of the experimental results, the second possibility is favoured.

First-principles density-functional method is used to study the recently high-pressure synthesized compound PtC. It is confirmed by our calculations that the platinum carbide has a zinc-blende ground-state phase at zero pressure and the rock-salt structure is a high-pressure phase. The theoretical transition pressure from zinc-blende to rock-salt is determined to be 52GPa. Furthermore, our calculation shows the possibility that the experimentally synthesized PtC by Ono et al. under high pressure condition might undergo a transition from rock-salt structure to zinc-blende after the pressure quench to ambient condition., A revised version

We employed accurate full potential density-functional theory and linearized augmented plane wave method to investigate the electronic properties and possible phase transitions of Cu3N under high pressure. The anti perovskite structure Cu3N is a semiconductor with a small indirect band gap at ambient pressure. The band gap becomes narrower with increasing pressure, and the semi-conducting anti ReO3 structure undergoes a semiconductor to semimetal transition at pressure around 8.0 GPa. At higher pressure, a subsequent semimetal to metal transition could take place above 15GPa with a structural transition from anti ReO3 to Cu3Au structure.

Using a 200 keV electron beam with the intensity ~7 × 1016 e nm−2 as an irradiation source, we investigated the irradiation effects on the microstructure of a new superconductor, Sr2CuO2+δCl2−y, by means of high-resolution transmission electron microscopy, electron energy loss spectroscopy (EELS) and energy dispersive analysis of x-rays (EDX). When the sample was illuminated along the [001] direction, a kind of modulated structure with modulation vector and wavelength λ = ~8.81 A was found to develop, while when the sample was illuminated along the [100] direction, there was no evidence of a transition of the modulated structure. The O K, Cu L2,3 EELS spectra and EDX data suggest that the modulated structure results from an ordered oxygen deficiency and the O vacancies are suggested to be located in the Cu–O plane.

A new type of flower-like ZnO nanostructure was prepared on a large scale through a very simple solvothermal method. The nanoflowers are assembled by many thin and uniform hexagonal-structured ZnO nanosheets, with a thickness of around 6 nm. The growth mechanism of the nanoflowers is discussed based on the reaction conditions. Room-temperature optical measurements reveal that such ZnO nanoflowers have very strong UV bandedge emission with a large Stokes shift and an asymmetrical band profile. This luminescence characteristic may be attributed to the anisotropic energy band structure of the quantum-confined ZnO nanosheets. r 2005 Elsevier B.V. All rights reserved.

K2NiF4-type Sr2CuO2+δCl2–y superconductor was synthesized with partial substitution of oxygen for apical chlorine using a high-pressure technique. This phase has been studied by transmission electron diffraction, convergent beam electron diffraction, x-ray powder diffraction, energy dispersive analysis of x-ray, electron energy loss spectroscopy and high-resolution electron microscopy. The crystal structure with a space group of I4/mmm has been determined, and the lattice parameters are obtained as a = b = 0.394 nm and c = 1.564 nm. Edge dislocations with Burgers vector are observed in the phase.

The structural and electrical properties of infinite-layer CaCuO2 (IL CaCuO2) under high pressure at room temperature were studied using a diamond anvil cell by in situ high pressure energy-dispersive X-ray diffraction with synchrotron radiation and by simultaneous resistance and electrical capacitance measurements. The results indicate that the primary crystal structure of IL CaCuO2 is stable under pressure up to 30 GPa with an anisotropic compressibility. The equation of state of IL CaCuO2 was obtained from the V/V0−P relationship based on the Birch–Murnaghan equation, which gives rise to a bulk modulus B0=96 GPa in the low pressure range below 6 GPa, and B0=186 GPa at pressures from 6 to 30 GPa for IL CaCuO2. The resistance and capacitance measurements of IL CaCuO2 up to 20 GPa revealed several unusual changes. There is an abrupt resistance drop in the pressure range of 3–6 GPa followed by an abnormal hump occurring around 12 GPa with increasing pressure. Corresponding changes were also observed in the dependence of capacitance on pressure. The former drop is attributed to an isostructural phase transition as observed in the synchrotron radiation experiments. The latter is considered to be related to an electronic structure transition resulting from the anisotropic compression of the IL CaCuO2 unit cell under high pressure.

Using pulse echo overlap measurement, the elastic behavior of amorphous carbon has been studied at ambient and low temperatures. The smaller ratio BIG of the bulk modulus to shear modulus and smaller Poisson's ratio sigma at room temperature indicate that there is an intrinsic stiffening of transverse acoustic phonons in the amorphous carbon. The acoustic velocity and attenuation for longitudinal modes have been measured between 2.1 and 300 K at three frequencies of 7, 21 and 35 MHz, respectively. Their frequency and temperature dependence are observed. The elastic constant C-11 increases with decreasing temperature and show enhanced stiffening at low temperatures. In the 130-220 K region, the abnormal change and effect of longitudinal velocity and attenuation with temperature and frequency, and a phase transition associated with structure relaxations are discussed. (C) 2003 Elsevier Science Ltd. All rights reserved.

The nominal compositions and structures of the compounds La2-2xCa1+2xMn2O7 (x=0.5 and 0.25) prepared by solid-state reaction have been studied by transmission electron microscopy and high-resolution electron microscopy. Besides the observation of the major phase of a two-layer structure in the nominal composition La1.0Ca2.0Mn2O7, the embedded n = 3, n = 4 Ruddlesden-Popper phases and La rich phase in the two-layer structure were observed as defects. No layered structure was observed in the nominal composition La1.5Ca1.5Mn2O7. Instead, a major phase of orthorhombically distorted perovskite, a minor phase of an ideal cubic perovskite, and a small fraction of calcium-oxide were observed in the sample. The coexistence of the orthorhombic phase and ideal cubic perovskite phase, as well as the same orthorhombic phase with perpendicular directions, was observed in the nominal composition La1.5Ca1.5Mn2O7. (C) 2002 Elsevier Science B.V. All rights reserved.

The structural evolutions of glassy carbon (GC) and graphitized glassy carbon (GGC) treated under high temperatures and high pressures have been studied by energy-dispersive x-ray diffraction in a diamond anvil cell. The equations of state of GC and GGC are determined from x-ray density data. GC has a higher bulk modulus than that of GGC. It is found that the two-dimensional order of stacked layers in GC decreases with increasing the stresses, and the orientated layers merge with the disorientated layers at higher pressures, in which it can also be attributed to the appearance of a bump in the electrical resistance measurements under high pressures.

The structural, magnetic and transport properties of the compounds Sr2(Fe1−xMnx)MoO6 (0 ≤ x ≤ 0.45) have been studied. The saturated magnetization, Curie temperature and low-field magnetoresistance of the compounds decrease with x, while the resistivity increases by several orders of magnitude when x exceeds a critical value. A positive magnetoresistance has been observed for x = 0.45. A possible percolation mechanism is proposed to elucidate the observations; it also suggests a coexistence of (Mn3+, Mo5+) and (Mn2+, Mo6+) valence pairs and a saturated substitution of Mn3+ for Fe3+.

The magnetic and magnetoresistance properties of Lao(0.825)Sr(0.175)MnO(3) powder compact prepared by the mechanical alloying method and high temperature high pressure treatment have been investigated. Analysis by means of x-ray diffraction and scanning electron microscopy show that the La0.825Sr0.175MnO3 powder has an average grain size of 100 nm and has been partly non-crystallized by mechanical alloying. Compared with the crystal and general nanogranular samples of the same material. the powder compact is considerably different in both magnetic and magnetoresistance properties.

An ideal n = 3 member of the group of Ruddlesden?Popper (RP) phases Ca4Mn3O10 was obtained by solid-state reaction under high pressure. This phase has been studied by transmission electron microscopy, convergent beam electron microscopy, high-resolution transmission electron microscopy, and parallel electron energy-loss spectroscopy. The lattice parameters are derived as a = b = 0.37 nm and c = 2.69 nm with the space group I4/mmm, which is the space group of the ideal RP phase.

C3N4H4 was treated at 6.0 GPa and 1500 °C for 2.5 min. Powder x-ray measurement shows that the sample is decomposed and a hexagonal graphite phase forms. Transmission electron microscopy studies show that small amounts of diamond and amorphous carbon phase coexist with the graphite phase. Parallel electron energy-loss spectroscopy analysis was also carried out for these phases.

We report in situ high-pressure studies up to 1.0 GPa on MgB(2) superconductor which had been synthesized at high pressure. The as-prepared sample is of high quality as regards having a sharp superconducting transition (T(C)) at 39 K. The in situ high-pressure measurements were carried out using a Be-Cu piston-cylinder-type instrument with a mixed oil as the pressure- transmitting medium, which provides a quasi- hydrostatic pressure environment at low temperature. The superconducting transitions were measured using the electrical conductance method. It is found that T, increases with pressure in the initial pressure range, leading to a parabolic- like T(C)-P evolution.

We have carried out DC magnetization measurements on spherical glassy carbon exposed to high temperatures and high pressures. The observed magnetic signals clearly depend on the sintering temperature. On the basis of the graphitization temperature (around 1400oC), the behaviour can be classified into three regions: (1) paramagnetism in the no-graphitization region; (2) ferromagnetism in the near-graphitization region; (3) diamagnetic behaviour after graphitization. The magnetic transitions associated with the process of graphitization are discussed.

C 3 N 4 H 4 was treated at 6.0 GPa and 1500 °C for 2.5 min. The powder X-ray measurement shows that the sample is decomposed and a hexagonal graphite phase forms. Transmission electron microscopy studies show that a small amount of diamond and amorphous carbon phases coexists with the graphite phase. Parallel electron energy loss spectroscopy analysis was also carried out for these phases.

Using diamond anvil cell technique, energy-dispersive X-ray diffraction and Raman spectroscopy were employed to study pressure induced phase transitions in nanocrystalline selenium up to 30 GPa. A complex phase transition behavior was observed, with lower transition pressure and more phase transitions than in conventional coarse-grained Se. This is considered a new kind of pressure induced phase transition behavior for a nanocrystalline material.

H-c2 of MgCNi3 has been determined from the specific heat C and resistivity rho measurements in the same sample. The results from rho are nearly identical with those determined from the anomaly in C. Furthermore, utilizing the relation gamma(H) proportional to H and the value of dgamma/dH, the obtained value of H-c2 is the same as that by the WHH model, if the spin paramagnetic effect and the spin-orbit interaction are taken into account. The results of this comparison have strong implications on the order parameter of MgCNi3.

Recently, A2B3 type strong spin orbital coupling compounds such as Bi2Te3, Bi2Se3 and Sb2Te3 were theoretically predicated to be topological insulators and demonstrated through experimental efforts. The counterpart compound Sb2Se3 on the other hand was found to be topological trivial, but further theoretical studies indicated that the pressure might induce Sb2Se3 into a topological nontrivial state. Here, we report on the discovery of superconductivity in Sb2Se3 single crystal induced via pressure. Our experiments indicated that Sb2Se3 became superconductive at high pressures above 10 GPa proceeded by a pressure induced insulator to metal like transition at ~3 GPa which should be related to the topological quantum transition. The superconducting transition temperature (TC) increased to around 8.0 K with pressure up to 40 GPa while it keeps ambient structure. High pressure Raman revealed that new modes appeared around 10 GPa and 20 GPa, respectively, which correspond to occurrence of superconductivity and to the change of TC slop as the function of high pressure in conjunction with the evolutions of structural parameters at high pressures.

We conducted in situ angle dispersive high pressure x-ray diffraction experiments on Sr3Ir2O7 up to 23.1 GPa at 25 K with neon as the pressure transmitting medium. Pressure induces a highly anisotropic compressional behavior seen where the tetragonal plane is compressed much faster than the perpendicular direction. By analyzing different aspects of the diffraction data, a second-order structural transition is observed at approximately 14 GPa, which is accompanied by the insulating state to nearly metallic state at 13.2 GPa observed previously (Li et al 2013 Phys. Rev. B 87 235127). Our results highlight the coupling between electronic state and lattice structure in Sr3Ir2O7 under pressure.

An ideal n=3 member of Ruddlesden–Popper (RP) phase Ca4Mn3O10 was obtained by solid-state reaction under high pressure. This phase has been studied by transmission electron microscopy, convergent beam electron microscopy, high-resolution transmission electron microscopy, and electron energy loss spectroscopy. The lattice parameters are derived as a=b=0.37 nm and c=2.69 nm with a space group of I4/mmm, which is the space group of ideal RP phase. The advantages of high pressure sintering are discussed.

The MgB2 intermetallic superconductor obtained under high pressure, which has the transition temperature of above 39 K, has been studied by scanning electron microscopy (SEM), transmission electron microscopy and parallel electron energy-loss spectroscopy (EELS). From the SEM, it can be seen that the bulk compound is highly dense and the grains are connected compactly. The size of single crystal is at the magnitude of similar to mum. The high resolution transmission electron microscopy image of [001] zone axis clearly shows the hexagonal planes of the constituent atoms. The EELS spectrum of B shows the peaks of a and antibonding bonds. The EELS results show a good agreement with the theoretical band structure calculations and the hole doping in the B sigma (P-xy) bonding bands. (C) 2001 Elsevier Science B.V. All rights reserved.

In situ high pressure energy dispersive X-ray diffraction measurements on layered perovskite-like manganate Ca 3 Mn 2 O 7 under pressures up to 35 GPa have been performed by using diamond anvil cell with synchrotron radiation. The results show that the structure of layered perovskite-like manganate Ca 3 Mn 2 O 7 is unstable under pressure due to the easy compression of NaCl-type blocks. The structure of Ca 3 Mn 2 O 7 underwent two phase transitions under pressures in the range of 0~35 GPa. One was at about 1.3 GPa with the crystal structure changing from tetragonal to orthorhombic. The other was at about 9.5 GPa with the crystal structure changing from orthorhombic back to another tetragonal.

Single-phase multiferroic BiMnO 3 ceramic was synthesized via high-pressure and high-temperature solid-state reaction. Microstructure modification accompanied by emergence of superlattice due to electron-beam irradiation was observed wherein by means of electron diffraction (ED) combined with high-resolution transmission electron microscopy (HRTEM). It was clearly evidenced that the well-established C2 monoclinic substructure ( I ) of BiMnO 3 is metastable and prone to transform into a new pseudo-cubic superstructure ( I* ) with larger unit cell and higher symmetry. Magnetic characterization manifesting a unique ferromagnetic phase transition at 103 K has corroborated our speculation that as-prepared BiMnO 3 ceramic is free of polymorphism at room temperature. Weak ferromagnetism characterized by a well-saturated ferromagnetic hysteresis loop was manifested in the bulk BMO with Curie temperature T C ∼105 K. Modestly saturated ferroelectric hysteresis loops were observed at room temperature. In light of comprehensive evaluation, we can conclude the synthetic BiMnO 3 ceramic displays ferromagnetic and ferroelectric ordering simultaneously, i.e. ferroelectromagnetism below its ferromagnetic Curie temperature T M ∼105 K.