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The influence of Mg content on the mechanical properties, degradation behavior, in vitro cell adhesion, and in vivo behavior of as-extruded Zn–xMg–0.1Ca (x = 0.5 wt%, 1.0 wt%, 1.5 wt%) alloys was investigated. A high Mg content could increase the volume fraction of the hard Mg2Zn11 phase distributed at grain boundaries. This condition could significantly improve yield strength and ultimate tensile strength. Mg addition could adjust the degradation rate of Zn alloys and influence cytocompatibility. ZnMg1Ca0.1 alloy showed the highest adhesion density of bone marrow-derived mesenchymal stem cells (BMSCs) because the degradation rate of ZnMg1Ca0.1 alloy could supply appropriate pH and [Zn2+] for BMSCs. Mg addition could improve the cytocompatibility of Zn Mg Ca alloys. However, a Mg content threshold was observed, and the Mg content should be exactly controlled. Combined with the mechanical properties, the degradation rate of zinc alloy implants could be adjusted to match the healing of tissues by adding Mg. In vivo results showed that the degradation rate of the optimized Zn Mg Ca alloy could match the healing of local tissues or organs. Animal implant results revealed alloy safety.

In this study, heat treatment and extrusion were used respectively to optimize the microstructure of a novel Mg-2Y-1Zn-0.4Zr alloy, and its mechanical property, degradation behavior and cytocompatibility were investigated. Stress-strain curves showed that both heat treatment and extrusion could improve the mechanical properties of the alloy. Electrochemical results indicated that, comparing with as-cast specimen, the heat treated and as-extruded samples showed lower corrosion rate and less susceptibility to pitting corrosion. The cytotoxicity was evaluated using the methylthiazolyl diphenyltetrazolium bromide method via mouse fibroblast L929 cells. The results revealed that the cytocompatibility of Mg-2Y-1Zn-0.4Zr alloy was enhanced by heat treatment and extrusion. Besides, as-extruded alloy showed favorable mechanical property, the best degradation behavior and cytocompatibility which suggests that as-extruded may be a good candidate to be used in biomedical applications.

Ultra-fine-grained Zn-0.5Mn alloy was prepared by multi-pass hot extrusion. Minimum grain size of the Zn-0.5Mn alloy was about 0.35 µm, it exhibited room temperature superplasticity. During multi-pass extrusion, the pinning force of MnZn13 rendered the subgrains stable and restrained grain growth. The ultra-fine grain was finally formed.

The mechanism of CO2 dissociation during entry in the Mars atmosphere is experimentally investigated. A hydrogen–oxygen combustion-driven shock tube is used to simulate physical and chemical condit...

This paper investigates the structural and magnetic properties of hexagonal Ba(Ti1-xFex)O3-delta (x=0.3 and 0.7) ceramics, synthesized with solid-state reaction method. Transmission electron microscope investigations reveal that structural phase separation featured by non-modulated and modulated phases is identified by the electron diffraction patterns taken along [0 0 1] zone axis in x=0.3 sample (BTF30). While for x=0.7 sample (BTF70), a pure phase with commensurate and incommensurate modulations at different directions is identified. The superstructure peaks observed in their X-ray diffraction patterns are verified by their individual commensurate modulation, q(s)=1/2 (31-2) in the modulated phase of BTF30 and q(4,-1)=4/9(3 0 4)-(0 0 1) in BTF70. In addition to the room-temperature weak ferromagnetism of BTF30 and paramagnetism of BTF70, spin glass transitions with T-f=3.4 K for the former and T-f=33.6 K for the latter are observed. On the basis of the structural characteristics, the influence of O1 and O2 vacancies on magnetic and dielectric properties of the doped system is discussed. (C) 2010 Elsevier B.V. All rights reserved.

Solid state reaction method is used to synthesize Ba(Tii-xTMx)O3-delta (TM = Fe, Mn and Co) and (Ba1-ySry)(Ti1/3Fe2/3)O3-delta ceramics. The X-ray diffraction, scanning electron microscopy and transmission electron microscopy investigations reveal that structural evolutions from an orthorhombic BaTiO3 to a hexagonal Ba(Ti1-xTMx)O3-delta, a hexagonal to a rhombohedral in Ba(Ti1-xMnx)O3-delta, and a hexagonal to a pseudo-cubic transition in (Ba1-ySry)(Ti1/3Fe2/3)O3-delta are induced by increasing the doping concentration. Due to the oxygen vacancies derived from acceptor doping, nanoscale domains of incommensurate modulation (ICM) resultant are commonly observed in the hexagonal Ba(Ti1-xTMx)O3-delta compounds. The newly discovered rhombohedral Ba(Ti1/3Mn2/3)O3-delta having characteristic of face-sharing prism corner-connected by oxygen atoms is a typical example in searching for novel multiferroics. Discrepancies between the ionic radii of the B- and A-site dopants and that of Ti and Ba as a function of the doping concentrations, i.e., the effects of oxygen vacancies and the electronic configurations of the dopants, are concluded to be the driving forces for the structural transitions. (c) 2010 Elsevier B.V. All rights reserved.

Activated carbon was treated at 5.0 GPa up to 1600 degrees C and the structural evolution in the graphitization process was investigated. The graphitization temperature is reduced to 1200 degrees C at 5 GPa, as reflected by x-ray diffraction patterns. Honeycomb-like structures come into being in the high-pressure sintering temperature range of 1000-1100 degrees C and slice-like structures appear after graphitization. Raman frequency and half width drop drastically near the graphitization temperature, and the appearance of D and D' lines indicates there are still some disorder structures in the graphitized activated carbon. (C) 2009 Published by Elsevier Ltd

Activated carbon was treated at 5.0 GPa up to 1600 °C, and the electrical property evolution in the graphitization process was investigated. The change of structure results in the corresponding electrical property transition. For the samples at low high-pressure sintering temperature, the variable-range hopping is the main electrical transportation mechanism. The graphitized activated carbon is a semimetal while the high-pressure sintering temperature is lower than 1300 °C and behaves non-Fermi-liquid property at higher sintering temperature. The ratio of resistivity at ∼5.0 and ∼300.0 K versus high-pressure sintering temperature is drastically decreasing near the graphitization temperature, which indicates that the insulator–metal transition occurs in the sintering temperature range of 900–1000 °C.

La2/3Ca1/3MnO3 and Se2FeMoO6 nano-crystalline powders were pre-prepared using the polymer-network gel method, and the average grain sizes of La2/3Ca1/3MnO3 and Se2FeMoO6 were about 40 and 50 nm, respectively. A series of La2/3Ca1/3MnO3/Se2FeMoO6 nano-crystalline composites (molar ratio 1:1) were successfully synthesized under high pressure (4 GPa) and different treating temperatures. Due to the compositive influence of the smaller grain sizes, the Curie transition temperatures T-C (similar to 225 K) for all composites are lower than that of the pure phase La2/3Ca1/3MnO3. For the sample synthesized at the optimum conditions, the magnetoresistance value is close to 32% at 3 T and 5 K. (c) 2007 Elsevier B.V. All rights reserved.

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.

We address the role of apical oxygen that plays the bridges linking charge reservoir and CuO2 conducting layers for high Tc superconductors (HTS). The presentation will introduce our recent work on high pressure synthesis of novel superconductors in the A–Cu–O simple system by tuning apical oxygen content and arrangement (A represents alkaline earth element). The topic will focus on 214 type compounds highlighting apical oxygen as a novel doping mechanism in oxychloride HTS, or dopant at a partially occupied apex, especially the unusual enhancement of Tc up to 95 K in a monolayered HTS by improving ordering state.

BaTiO3 ceramics with a grain size of 30 nm were prepared at 6 GPa, 1,273 K using a three-step high pressure sintering method. The sintered bulk is uniform and the relative density is above 96% of the theoretical value. Similar to normal BaTiO3, successive phase transitions were observed in 30 nm BaTiO3 ceramics by X-ray diffraction method with the change of temperature. After annealing in O2, a broadened ferroelectric transition was obtained at 398 K and the relative dielectric constant is 1,700 at 10 kHz.

By measuring O 1s and Cu 2p 3/2 absorption edges of Sr 2 CuO 2+ δ Cl 2− y using orientation-dependent high-energy electron energy-loss spectroscopy, the changes of the unoccupied electronic structure close to the Fermi level induced by stoichiometry variations have been explored. An interesting hole redistribution between the in-plane O 2p orbitals and apical O 2p orbitals induced by the doping level has been revealed in this system. For the low-doped samples in which superconductivity is absent, the holes reside predominantly on the oxygen sites of the CuO 2 plane, while for the high-doped samples in which superconductivity appears, considerable holes are found to enter the apical oxygen sites. This result reveals clearly that the apical O 2p holes play an important role in the occurrence of superconductivity in the ‘apical oxygen doped’ Sr 2 CuO 2+ δ Cl 2− y system.

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.

In-situ high-pressure energy dispersive X-ray diffraction measurements on CuBa 2- Ca 3 Cu 4 O 10 + δ (Cu-1234) have been performed by using diamond anvil cell (DAC) device with synchrotron radiation. The results suggest that the crystal structure of Cu-1234 superconductor is stable under pressures up to 34 GPa at room temperature. According to the Birch–Murnaghan equation of state, the bulk modulus is obtained to be ~ 150 GPa.

Crystallographic cracking behavior was studied on three-point-bending specimens of silicon single-crystal wafer having (1(1) over bar 0) [11(2) over bar] -oriented precrack. Crystallographic cracking occurred on alternating {111} planes after traversing about 500 mum from crack front at the brittle-ductile-transition temperature, and the main crack was almost parallel to the loading axis. The preferentially activated slip systems ahead of the crack tip resulted in the characteristic fracture in the specimens. The experimental results could be well explained by calculating the shear stress on all possible tetrahedral slip planes around the crack tip. (C) 2003 Elsevier B.V. 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 manganate with nominal composition La1.0Ca2.0Mn2O7 was prepared using a standard solid-state reaction method under ambient pressure. The structure of the compound was investigated using powder X-ray diffraction, Rietveld analysis and TEM experiments. The results show that the compound forms multiphase mixtures comprising the layered perovskite manganate La1.0Ca2.0Mn2O7 with 91.3% weight fraction as majority phase, the perovskite manganate La0.5Ca0.5MnO3 with weight fraction 8.7% as the minority phase. The occurrence of weak magnetization at 250 K and the presence of weak magnetization in the lower temperature region of 5-135 K are linked to the perovskite manganate La0.5Ca0.5MnO3 and the layered perovskite manganate La1.0Ca2.0Mn2O7, respectively. The magnetoresistance (MR) occurred in the lower temperature range arises mainly from the layered perovskite manganate La1.0Ca2.0Mn2O7. (C) 2002 Elsevier Science B.V. All rights reserved.

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.

In situ high-pressure energy dispersive X-ray diffraction experiment on Zn3N2 has been performed by using a diamond anvil cell instrument with synchrotron radiation at room temperature. The results showed that the structure of Zn3N2 is stable in the experimental pressure range up to 25.2 GPa.

We have synthesized a single-phase Sr2CuO3+delta Superconductor of T-c 75 K with K2NiF4 structure under high-pressure showing so far rarely formed partially occupied "apical oxygen" which also acts as the dopant. After post annealing the as-prepared sample from 150 degrees C to 300 degrees C at ambient, the superconducting transition temperature (T-c) could be systematically enhanced up to 95 K. Transmission electron microscopy (TEM) measurements on the Sr2CuO3+delta superconductors revealed a series of modulated structure phenomena resulting from dopant ordering. The distribution geometry of dopant such as the partially occupied apical oxygen here can be an additional route to reach further higher T-c. (C) 2007 Elsevier B.V. All rights reserved.

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.

Using the apical oxygen doping mechanism, i.e. a partial substitution of divalence O for the monovalence Cl , a p-type copper oxychloride superconductor, Sr 2 CuO 2+δ Cl 2-y, was synthesized at 1050°C under 6.0 GPa for 1h. The X-ray powder diffractions show that the main phase has a tetragonal structure with a=3.93Å, c=15.65 Å. The magnetic susceptibility as well as resistance measurements indicated that the bulk superconducting transition temperature of the sample is 30K.

We report the property studies of a MgB2 superconductor with high critical current density. The MgB2 superconductor was readily fabricated through a direct high-pressure synthesis of the respective elements. The obtained high-density MgB2 undergoes a sharp superconducting transition at 39 K. The bulk critical current density (Jc) of the sample was calculated on the basis of Bean's critical state model, and rather high critical current densities over a wide temperature range were obtained in comparison with the ambient prepared samples. The results highlight that high-pressure sintering would be a promising way to produce and search for this kind of intermetallic boride and the related superconductors.

Single-crystalline CaFe2As2 and (Ca1-xNax)Fe2As2 polycrystals (0 < x < 0.66) are synthesized and characterized using structural, magnetic, electronic transport, and heat capacity measurements. These measurements show that the structural/magnetic phase transition in CaFe2As2 at 165 K is monotonically suppressed by the Na doping and that superconductivity can be realized over a wide doping region. For 0.3 < x < 0.36, the magnetic susceptibilities indicate the possible coexistence of the spin density wave (SDW) and superconductivity. Superconducting phases corresponding to the Na doping level in (Ca1-xNax)Fe2As2 for nominal x = 0.36, 0.4, 0.5, 0.6, and 0.66, with Tc = 17, 19, 22, 33, and 34 K, respectively, are identified. The effects of the magnetic field on the superconductivity transitions for x = 0.66 samples are studied from which high upper critical fields H-c2 approximate to 103 T is deduced. A phase diagram of the SDW and superconductivity as a function of the doping level is thus presented.

A series of new Sr2-xBaxCuO3+delta (0 < x < 0.6) superconductors were prepared using high-pressure and high-temperature synthesis. A Rietveld refinement based on powder x-ray diffraction confirms that the superconductors crystallize in the K2NiF4-type structure of a space group I4/mmm similar to that of La2CuO4 but with partially occupied apical oxygen sites. It is found that the superconducting transition temperature T-c of this Ba substituted Sr2CuO3+delta superconductor with constant carrier-doping level, i.e., constant delta is controlled not only by order/disorder of apical-O atoms but also by Ba content. T-c(max)=98 K is achieved in the material with x=0.6 that reaches the record value of T-c among the single-layer copper oxide superconductors and is higher than T-c=95 K of Sr2CuO3+delta with optimally ordered apical-O atoms. There is Sr-site disorder in Sr2-xBaxCuO3+delta which might lead to a reduction in T-c. The result indicates that another effect surpasses the disorder effect that is related either to the increased in-plane Cu-O bond length or to elongated apical-O distance due to Ba substitution with larger cation size. The present experiment demonstrates that the optimization of local geometry out of the Cu-O plane can dramatically enhance T-c in the cuprate superconductors.

The nominal composition of Sr{sub 0.39}CoO{sub 2}, prepared by a low-temperature ion exchange technique, has been systematically studied by transmission electron microscopy, energy dispersive x-ray spectroscopy (EDX), and electron-energy-loss spectroscopy (EELS). Besides a well-defined {radical}(3)a{sub p}x{radical}(3)a{sub p} modulated structure, a series of long periodic modulated structures (n{radical}(3)a{sub p}x3a{sub p}) was revealed by high-resolution transmission electron microscopy (HRTEM) in some microzones, which are induced by alternate position ordering of strontium ions. The results of EDX analyses confirm the variation of Sr content in corresponding modulated phases. Moreover, the L{sub 3}/L{sub 2} intensity ratio of Co-L{sub 2,3} edges in the EELS spectra indicates the variation of Co ionic valence state induced by the different contents of Sr cations. Based on the {radical}(3)a{sub p}x{radical}(3)a{sub p} superstructural model, we propose the possible corresponding structural models in this paper. The simulated HRTEM images, based on those models, are consistent with experimental ones. In addition, several phase separations and some structural defects were observed in the sample.

The structural evolution of biferroic $\mathrm{Bi}\mathrm{Mn}{\mathrm{O}}_{3}$ caused by electron-beam irradiation has been systemically studied by means of electron diffraction (ED), high-resolution transmission electron microscopy (HRTEM), electron energy-loss spectroscopy (EELS), and energy dispersive analysis of x-ray (EDX). The ED and HRTEM observations demonstrate clearly that the well-known $C2$ monoclinic form of $\mathrm{Bi}\mathrm{Mn}{\mathrm{O}}_{3}$ is easily and irreversibly transformed to another modulated form by electron-beam irradiation. This irradiation-induced form shows an apparently higher symmetry and can be described by a body-centered pseudocubic superstructure with $a\ensuremath{\approx}b\ensuremath{\approx}c\ensuremath{\approx}15.8\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ and $\ensuremath{\alpha}\ensuremath{\approx}\ensuremath{\beta}\ensuremath{\approx}\ensuremath{\gamma}\ensuremath{\approx}90\ifmmode^\circ\else\textdegree\fi{}$. The EELS and EDX measurements reveal a small decrease of $\mathrm{O}∕\mathrm{Mn}$ ratio, but no change of $\mathrm{Bi}∕\mathrm{Mn}$ ratio in the irradiation-induced form as compared with the $C2$ monoclinic form. From the decrease of the $\mathrm{O}∕\mathrm{Mn}$ ratio, it can be concluded that the irradiation-induced form is produced from ordered oxygen deficiencies. A possible structure model is proposed.

Using the apical oxygen doping mechanism, i.e. a partial substitution of divalence O for the monovalence Cl, a p-type oxychloride cuprate superconductor, Sr2CuO2+xCl2-y, was synthesized at high pressure high temperature. The x-ray diffraction refinement suggests the superconductor crystallizes into a 0201 structure with space group I4/mmm and lattice parameters being a=3.92A, c=15.6 A. The magnetic susceptibility as well as resistance measurements indicated that the bulk superconductivity with transition temperature 30K was achieved in the sample., accepted by physica c

Series samples of ${\mathrm{Sr}}_{2\ensuremath{-}x}{\mathrm{Ba}}_{x}{\mathrm{FeMoO}}_{6}$ have been synthesized using conventional solid-state reaction, and the effect of Ba content on the initial magnetizations of the samples has been studied. The measured saturation magnetizations of the samples show that the degree of antisite of Fe and Mo decreases with increasing Ba content. Structural stability and electrical properties of two samples of ${\mathrm{Sr}}_{2\ensuremath{-}x}{\mathrm{Ba}}_{x}{\mathrm{FeMoO}}_{6}$ under high pressure at room temperature have been studied using energy dispersive x-ray diffraction with synchrotron radiation and resistance and capacitance measurements. The x-ray diffraction results show that the structures of ${\mathrm{Sr}}_{2\ensuremath{-}x}{\mathrm{Ba}}_{x}{\mathrm{FeMoO}}_{6}$ remain stable in the measured pressure range of about 0--40 GPa. The equations of state of the two samples are obtained from the ${V/V}_{0}\ensuremath{-}P$ relationship based on the Birch-Murnaghan equation. The bulk moduli ${B}_{0}$ of the two samples are calculated according to the Birch-Murnaghan equation assuming that their first order derivatives ${B}_{0}^{\ensuremath{'}}$ are equal to 4. The electrical resistance for the samples shows an abrupt drop at about 2.3--3.8 GPa, which might be caused by a change in the electronic structure induced by high pressure.

A series of new superconductors Sr 2− x Ba x CuO 3+ δ ( x ⩽ 0.6) were prepared under high pressure high temperature. The superconductors crystallize into K 2 NiF 4 -type structure of I 4/mmm space group similar to the classical La 2 CuO 4 but with partially occupied apical oxygen. It is found that T c of this barium doped Sr 2 CuO 3+ δ superconductor is associated with the ratio of A-site cation substitution while keeping at optimal carrier doping level. The superconducting transition temperature with T c max = 98 K which represents the record high T c in the single-layer copper oxide superconductors was achieved in this material.

We have successfully synthesized a new 0201-type superconductor Sr 2 CuO 2+ δ Cl 2− y under high pressure using the “apical oxygen doping” mechanism, i.e., partially substituting the oxygen for chlorine at the “apical” site. The X-ray diffraction refinements as well as electron microcopy observations suggest that the new superconductor crystallizes into a K 2 NiF 4 structure with tetragonal unit cell of a = 3.92 A, c = 15.65 A. Magnetic susceptibility as well as resistance measurement demonstrates the presence of a bulk superconductivity with transition temperature ( T c ) at 30 K in Sr 2 CuO 2+ δ Cl 2− y superconductor.

We discuss the evolution of superconducting transition temperature T c with the ordering state at the apical oxygen layer of a high temperature superconductor (HTS). This study became available in Sr 2 CuO 3+ δ superconductor with K 2 NiF 4 structure showing so far rarely formed partially occupied apical oxygen which also acts as the dopant. With observation of a series of modulation structures at apical oxygen layer, we found a well-defined links between T c (from 75 to 95 K) and modulated structures. We address that the distribution geometry of dopant such as the partially occupied apical oxygen here can be an additional route to reach further higher T c .

We have measured the magnetic properties on the high quality polycrystalline sample of the recently discovered ternary carbide superconductor MgCNi3. The lower critical field, the upper critical field and the thermodynamic critical field were estimated. The coherence length, penetration depth, and the Ginzburg–Landau parameter were calculated, respectively.

The elastic anisotropy in hot-pressed samples of {beta}-Si{sub 3}N{sub 4} monolithic polycrystalline composites and in composite with 5 to 35% {beta}-Si{sub 3}N{sub 4} whiskers have been investigated at room temperature by high precision acoustic interferometry. All of the samples, including the monolithic Si{sub 3}N{sub 4}, show anisotropy characterized as transverse isotropic about the hot-pressing (HP) direction and are described using the five elastic stiffness moduli for hexagonal symmetry. The principal anisotropy is revealed in the shear modulus difference, (C{sub 66} {minus} C{sub 44})/C{sub 44}, which increases from 7% in the monolithic sample to 15% in samples with 10% or more whiskers. All the stiffness moduli except for C{sub 44} increase with the addition of whiskers. Young`s modulus in the HP direction is 5% smaller than in the HP plane in all samples. The whiskers enhance the shear anisotropy produced by the in situ elongated {beta}-grains.

We discussed the high pressure improvement on superconducting transition temperature (Tc) related to the ordering at the apical oxygen layer of a high temperature superconductor (HTS). This study became available in the high pressure synthesized Sr2CuO3+δ superconductor with K2NiF4 structure showing so far rarely formed partially occupied apical oxygen which also act as the dopant of the HTS. The well-defined links between Tc and modulated structures suggests that optimizing the ordering at apical oxygen layer outside CuO2 plane is a promising way to further enhance Tc.

Temperature dependence of the dielectric constant of nano-grain BaTiO3 (BTO) ceramic has been investigated under hydrostatic pressure up to 5 GPa. We show that the paraelectric-ferroelectric phase transition temperature, which is represented by TC (Curie temperature point), decreases with pressure at a rate of dTC/dσ = -40.0 K/GPa for coarse grain ceramic and -34.3 K/GPa for ceramic with 60nm size grains. For the paraelectric-ferroelectric phase transition temperature, the variation of inter-granular stress with reducing grain size is considered the main factor causing the decrease of TC and the change of dTC/dσ. Adding the hydrostatic-pressure and inter-granular stress contributions to a Ginsburg-Landau-Devonshire (GLD) type thermodynamic theory provides a satisfactory explanation to our experimental results. Based on the GLD theory, a phase diagram, reflecting the relationship among the transition temperature, grain size and hydrostatic-pressure, has been established, which matches well with our experimental results.