We report a successful observation of pressure-induced superconductivity in a topological compound Bi 2 Te 3 with T c of ∼3 K between 3 to 6 GPa. The combined high-pressure structure investigations with synchrotron radiation indicated that the superconductivity occurred at the ambient phase without crystal structure phase transition. The Hall effects measurements indicated the holetype carrier in the pressure-induced superconducting Bi 2 Te 3 single crystal. Consequently, the first-principles calculations based on the structural data obtained by the Rietveld refinement of X-ray diffraction patterns at high pressure showed that the electronic structure under pressure remained topologically nontrivial. The results suggested that topological superconductivity can be realized in Bi 2 Te 3 due to the proximity effect between superconducting bulk states and Dirac-type surface states. We also discuss the possibility that the bulk state could be a topological superconductor.high-pressure effects | pressure-tuned conductivity | topological superconductors U tilizing high pressure can be a very powerful method to generate new materials states, as demonstrated by either highpressure synthesis of new compounds, or pressure-tuned unique electronic states, such as insulator metal transitions. High pressure is particularly effective in tuning superconductivity as it is well documented that the record high superconducting transition temperature T c for either elements (1) or compounds (2) is created with the application of pressure. Recently, topological insulators (TIs) have generated great interest in the area of condensed matter physics (3-8). These materials have an insulating gap in the bulk, while also possessing conducting gapless edges or surface states in the boundaries that are protected by the timereversal symmetry (8, 9). Similar to TIs, topological superconductors have a full pairing gap in the bulk and gapless Majorana states on the edge or surface (10-13, 18). Majorana Fermions (14), half of ordinary Dirac fermions, could be very useful in topological quantum computing (15-17), which is proscriptive for new concept information technology.

Shape memory and ferromagnetic shape memory effects in single-crystal Ni 2 MnGa thin films Heusler alloy Mn 2 NiGa has been developed by synthesizing a series of ferromagnetic shape memory alloys Mn 25+x Ni 50−x Ga 25 ͑x = 0-25͒. Mn 2 NiGa exhibits a martensitic transformation around room temperature with a large thermal hysteresis up to 50 K and a lattice distortion as large as 21.3% and has a quite high Curie temperature of 588 K. The martensite shows a high-saturated field up to 2 T. The excellent two-way shape memory behavior with a strain of 1.7% was observed in the single crystal Mn 2 NiGa. The magnetic-field-controlled effect created a total strain up to 4.0% and changed the sign of the shape deformation effectively.

Both experimental and theoretical studies have been carried out to study the structure and magnetic properties of Mn 2 NiGa alloys. We have found, instead of forming L2 1 structure where both A and C sites are occupied by Mn atoms, the alloy favor a structure where the C site is occupied by Ni atoms and Mn atoms at A and B sites. The electronic structures of both cubic austenite and tetragonal martensite Mn 2 NiGa were calculated by self-consistent full-potential linearized-augmented plane-wave ͑FP-LAPW͒ method. Austenite Mn 2 NiGa materials show ferrimagnetism due to antiparallel but unbalanced magnetic moments of Mn atoms at A and B sublattices. The magnetic moment of Mn atoms decrease greatly upon martensitic transformation to a tetragonal structure with a 50% reduction in Mn moments at the A site and almost completely suppressed Mn moments at B sites. Consequently, martensite Mn 2 NiGa alloys show ferromagnetic coupling. Different magnetic orderings in martensite and austenite also lead to very different temperature dependence, with which the abnormal behavior of magnetization upon martensitic transformation can be understood. In the offstoichiometric samples with composition between Ni 2 MnGa and Mn 2 NiGa, we show that additional Mn atoms that substitute for Ni atoms in Ni 2 MnGa have the same magnetic behaviors as Mn in Mn 2 NiGa phase, which successfully explains the dependence of the magnetization on Mn composition.

BaNi2As2, with a first order phase transition around 131 K, is studied by the angle-resolved photoemission spectroscopy. The measured electronic structure is compared to the local density approximation calculations, revealing similar large electronlike bands aroundM and differences alongΓ-X. We further show that the electronic structure of BaNi2As2 is distinct from that of the sibling iron pnictides. Particularly, there is no signature of band folding, indicating no collinear SDW related magnetic ordering. Moreover, across the strong first order phase transition, the band shift exhibits a hysteresis, which is directly related to the significant lattice distortion in BaNi2As2.

A good field to develop new materials with half metallicity is the quaternary Heusler alloys. The preferred route is to combine the compounds that have been already grown in Heusler structure. As a typical example, the quaternary LiMgPdSb-type CoFeMnSi have been investigated in detail. For the quaternary LiMgPdSb-type compounds, three nonequivalent structures exist. From the calculated density of state (DOS) results, it can be seen that one superstructure shows half metallicity. The second superstructure has a pseudogap at the Fermi level. The third superstructure shows metallic behavior. Based on the analysis of the measured XRD pattern and magnetization curve, we can deduce that the CoFeMnSi compound is crystallized in the structure where half metallicity occurs. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3062812

Sintering temperature effects on the energy‐storage properties in barium strontium titanate glass–ceramics have been studied by polarization hysteresis measurements. In phase development and microstructure evolution tests, it was found that with the increase of sintering temperature, the crystallinity degree of primary ferroelectric phase increases. Dielectric measurements revealed a rapid increase over the sintering temperature range from 800° to 830°C. This effect is believed to be due to the emergence of ferroelectric phase. The variation in dielectric constant with sintering temperature is attributed to the change in crystallization mechanism between surface and interior of glass–ceramics. Moreover, the charged and discharged energy densities for the glass–ceramic samples sintered at different temperatures were measured by the use of the Sawyer–Tower circuit under unipolar field. It has been shown that the low released energy density in glass–ceramics is mainly caused by interfacial polarization.

A series of BaTiO 3 (BT)-based ferroelectric glass-ceramics have been prepared via controlled crystallization by varying the Ba/Ti ratio in an aluminum silicate glass composition, and the subsequent microstructure, phase evolution, and dielectric properties have been investigated. X-ray diffraction indicated that an increasing Ba/Ti ratio promoted the crystallization of BaTiO 3 and BaAl 2 Si 2 O 8 from the glass matrix, and the cracking of glass-ceramics appears to be correlated to mismatch in the thermal expansion coefficient among BaTiO 3 , BaAl 2 Si 2 O 8 , and the glass matrix. In addition, it was found that increasing the Ba/Ti ratio facilitated the formation of a dendrite structure with obvious porosity. The change in the Ba/Ti ratio in the glass notably modified the dielectric properties: a high Ba/Ti ratio in the glass resulted in an increased dielectric constant and decreased breakdown strength.

A two-way magnetic field controlled shape memory effect has been observed in single crystals of CoNiGa with martensitic transformation temperature ranging from 205 to 341 K. Two-way shape memory with −2.3% strain has been obtained in free samples. By applying a bias field of up to 2 T, the shape memory strain can be continuously controlled from negative 2.3% to positive 2.2% giving it a total strain of 4.5%. The magnetic properties of CoNiGa show that it is a good shape memory material working at relatively high temperature of up to 450 K, and has a lower magnetic anisotropy than NiMnGa.