Crystal structure of Ti4Ni2C.

Single crystals of the inter-metallic phase with composition Ti4Ni2C were serendipitously obtained by high-pressure sinter-ing of a mixture with initial chemical composition Ti2Ni. The Ti4Ni2C phase crystallizes in the Fd m space group and can be considered as a partially filled Ti2Ni structure with the C atom occupying an octa-hedral void. Ti4Ni2C is isotypic with Ti4Ni2O, Nb4Ni2C and Ta4Ni2C, all of which were studied previously by means of powder diffraction.

Al0.88Cu0.94Fe0.18.

The inter-metallic phase with composition Al0.88Cu0.94Fe0.18 was synthesized by high-temperature sinter-ing of a mixture with initial chemical composition Al78Cu48Fe13. Al0.88Cu0.94Fe0.18 adopts the CsCl structure type in space-group Pm m. The structure analysis revealed that one site is co-occupied by Al and Cu with a ratio of 0.88 (5):0.12 (5) and the other is co-occupied by Fe and Cu with a ratio of 0.2 (4):0.8 (4). The Al/Cu⋯Fe/Cu separation is 2.5465 (13) Å.

Crystal structure of AlFe0.95.

Three B2-type inter-metallic AlFe1 - δ phases (0.18 < δ < 0.05) in the Al-Fe binary system were synthesized by smelting and high temperature sinter-ing methods. The exact crystal structure for δ = 0.05 was refined by single-crystal X-ray diffraction. The amount of vacancy defects at the Fe atom sites was obtained by refining the corresponding site occupancy factor, converging to the chemical formula AlFe0.95, with a structure identical to that of ideal AlFe models inferred from powder X-ray or neutron diffraction patterns.

The Al61.49Mn11.35Ni4 phase in the Al-Mn-Ni system.

An inter-metallic phase in the Al-Mn-Ni system crystallizing in space group Cmcm (No. 63) and refined formula Al61.49Mn11.35Ni4 (called the R' phase) has been synthesized by high-temperature sinter-ing of a mixture with initial chemical composition Al60Mn7Ni3. In comparison with the structure model of the previously reported R phase with composition Al60Mn11Ni4 [Robinson (1954 ▸). Acta Cryst. 7, 494-497], there are two mutually exchanged Mn and Ni sites together with one positionally disordered Al site [occupancy ratio 0.811 (8):0.121 (7)] and one partially occupied Mn site [s.o.f. 0.677 (5)] in the current structure model of the R' phase.

Natural djurleite with refined composition Cu61.39S32 revealing disorder of some Cu sites.

A djurleite crystal was discovered from a natural sample originally labelled as chalcocite. The djurleite crystal under investigation has a refined composition of Cu61.39S32, thus revealing a Cu deficiency compared to the originally reported Cu62S32 phase [Evans (1979). Z. Kristallogr. 150, 299-320], where all atomic sites are reported to be fully occupied. In addition, the current refinement revealed a splitting of eight of the Cu sites into pairs.

Electron Density Changes and Ultrafast Carrier Dynamics of the Antiferromagnetic Semiconductor MnPS3 through Magnetic Phase Transition.

Studying ultrafast dynamics provides us with a way to modify materials from the timescale of particle interaction, and the related research on antiferromagnetic semiconductors is still inadequate. Based on the electron density reconstruction, we achieve the visualization of magnetic interactions of bulk antiferromagnetic MnPS3 in the ground state, reveal the role of two atomic site occupations of S atoms in different magnetic phase transitions, and provide the theoretical and experimental support for modifying magnetic properties by selectively replacing the S atom. The ultrafast carrier dynamics can provide information from the excited state to the ground state. Based on time-resolved transmittance measurements, ultrafast carrier dynamics of MnPS3 are reported. The phonon-assisted gap transition driven by the electronic structure is characterized. The coupling relationship among electrons, spin, and phonons is established. Furthermore, the spin orientations within different phases are confirmed.

In situ observation of the electrochemical lithiation of a single MnO@C nanorod electrode with core/shell structure.

Transition metal oxides (TMOs) play a crucial role in lithium-ion batteries (LIBs) due to their high theoretical capacity, natural abundance, and benign environmental impact, but they suffer from limitations such as cyclability and high-rate discharge ability. One leading cause is the lithiation-induced volume expansion (LIVE) for "conversion"-type TMOs, which can result in high stress, fracture and pulverization. Using carbon layers is an effective strategy to provide effective volumetric accommodation for lithium-ion (Li+) insertion; however, the detailed mechanism is unknown. In order to clarify the working mechanism of nanoscale LIBs, herein, the discharge reactions in a nanoscale LIB were investigated through in situ environmental transmission electron microscopy (ETEM). Visualization of the Li+ insertion process of MnO@C nanorods (NRs) with core/shell structure (CSS) and internal void space (IVS) was achieved. The LIVE occurred in a consecutive two-step mode, i.e., a LIVE of the carbon layer followed by a co-LIVE of the carbon layer and MnO. No volume contraction of the IVS was observed. The IVS acted as a buffer relieving the stress of the carbon layer. The carbon layer with IVS simultaneously improved the cyclability and the high-rate discharge ability of the electrode, pointing to a promising route for building better TMO electrode materials.

Discovery of Dome-Shaped Superconducting Phase and Anisotropic Transport in a van der Waals Layered Candidate NbIrTe4 under Pressure.

The unique electronic structure and crystal structure driven by external pressure in transition metal tellurides (TMTs) can host unconventional quantum states. Here, the discovery of pressure-induced phase transition at ≈2 GPa, and dome-shaped superconducting phase emerged in van der Waals layered NbIrTe4 is reported. The highest critical temperature (Tc ) is ≈5.8 K at pressure of ≈16 GPa, where the interlayered Te-Te covalent bonds form simultaneously derived from the synchrotron diffraction data, indicating the hosting structure of superconducting evolved from low-pressure two-dimensional (2D) phase to three-dimensional (3D) structure with pressure higher than 30 GPa. Strikingly, the authors have found an anisotropic transport in the vicinity of the superconducting state, suggesting the emergence of a "stripe"-like phase. The dome-shaped superconducting phase and anisotropic transport are possibly due to the spatial modulation of interlayer Josephson coupling .

Effective Regulation of ZnO Surface Facets for Enhanced Photoluminescence Properties Assisted by Zinc Quaternary Ammonium Salts.

Novel ZnO twined-mushroom structures highly exposed in (001̅) planes were fabricated via a facile solvothermal synthesis with assistance of a zinc quaternary ammonium salt in the methanol-water solvent to show enhanced photoluminescence properties. A series of ZnO morphologies regulated with different surface facets were obtained in both MeOH-H2O and EtOH MeOH-H2O solvents respectively, tuning the proportion of alcohol. The self-aggregation mechanism was proposed based on the time-controlled experiment to evaluate the formation of twined-mushroom structures. The selective adsorptions of anions from zinc salt precursors determine the shape of subunits and direct the subunits, which act as building blocks to form the order aggregations.

Large Anisotropic Magnetocaloric Effect, Wide Operating Temperature Range, and Large Refrigeration Capacity in Single-Crystal Mn5Ge3 and Mn5Ge3/Mn3.5Fe1.5Ge3 Heterostructures.

At present, the studies on magnetocaloric properties are mainly based on polycrystalline materials, which is not enough to reveal and understand the origin of their magnetocaloric effect. In addition, finding new room temperature magnetocaloric materials is crucial to the development and application for room temperature magnetic refrigeration. Here, we report the magnetic transitions, magnetic anisotropy, and magnetocaloric properties of single-crystal Mn5Ge3 and Mn5Ge3/Mn3.5Fe1.5Ge3 heterostructures with six (100) surfaces and the [001] growth direction prepared using the Sn flux method. Mn5Ge3 (Mn3.5Fe1.5Ge3) undergoes a sharp paramagnetic-collinear ferromagnetic transition at 299 (332) K and weak collinear-noncollinear ferromagnetic transition at 65 (35) K. Owing to the distinct spin arrangements and magnetic moments of Mn5Ge3 and Mn3.5Fe1.5Ge3, the magnetic anisotropy of the single crystal is stronger than that of the heterostructure below 299 K. Moreover, a large anisotropic magnetocaloric effect, wide operating temperature range, and large refrigeration capacity near room temperature are obtained in these two materials, especially the magnetocaloric effect of the heterostructure presents a tablelike shape due to the adjacent paramagnetic-collinear ferromagnetic transitions of Mn5Ge3 and Mn3.5Fe1.5Ge3. Under 0-3 T, the maximum magnetic entropy change, operating temperature range, and refrigeration capacity of the single crystal (heterostructure) are 5.19 (2.96) J kg-1 K-1, 43 (57) K, and 223 (169) J kg-1 when H//c, respectively. These features make them candidates for room temperature magnetic refrigeration.

The structure of the aluminium-abundant γ-brass-type Al8.6Mn4.4.

An aluminium-abundant Al8Mn5/γ-brass-type inter-metallic with formula Al8.6Mn4.4, which is isotypic with γ-Al8Cr5 and γ-Al8V5, was discovered by high-temperature sinter-ing of an Al/Mn mixture with initial composition Al2Mn. Structure analysis revealed that one special position (Wyckoff site 18h in space group R m) is shared by Al and Mn, with refined site occupancy factors of 0.7 and 0.3, respectively. The present low-temperature Al8Mn5-type phase crystallizes in the centrosymmetric space group R m (No. 166), rather than R3m (No. 160) as previously reported for the same inter-metallic characterized by TEM measurements [Zeng et al. (2018 ▸). Acta Mater. 153, 364-376].

Crystal structure of the Al20Mn5.37Ni1.31 phase in the Al-Mn-Ni system.

The inter-metallic phase with composition Al20Mn5.37Ni1.31 (icosa-aluminium penta-manganese nickel) was synthesized by high-temperature sinter-ing of a mixture with initial chemical composition Al60Mn7Ni3. Al20Mn5.37Ni1.31 adopts the Co2Al5 structure type in space-group type P63/mmc, replacing the Co atoms with the transition-metal atoms Mn and Ni. Structure analysis revealed that one of the two transition-metal sites is partially occupied by Ni [refined occupancy 0.342 (2)] and the other is co-occupied by Mn and Ni with a ratio of 0.895 (14):0.105 (14). The present refined chemical composition is supported by complementary energy-dispersive X-ray fluorescence (EDX) analysis and is in agreement with the previously determined Al-Mn-Ni phase diagram [Balanetskyy et al. (2011 ▸). J. Alloys Compd, 509, 3795-3805].

Colossal Negative Linear Compressibility in Porous Organic Salts.

Negative linear compressibility (NLC) is a common sense violation (that is, crystal phases expand in one or more directions under hydrostatic compression). The excellent NLC performance of crystal materials is intrinsically related to the geometric structure of its skeleton. Here, we discovered a crystalline porous organic salt (CPOS-1); high-pressure X-ray diffraction experiments reveal that the CPOS-1 shows colossal NLC (Kc = -90.7 T Pa-1) behavior along the c axis. This incredible performance arises from the flexible "supramolecular spring" formed by the charge-enhanced N-H+···-O-S hydrogen bond interaction between the anionic sulfonate and the cationic ammonium ion. Furthermore, we reveal the relationship between this rare NLC behavior and single crystal proton conductivity using high-pressure electrochemical impedance spectroscopy (EIS) method. We believe that NLC behavior research on such inexpensive and readily available porous organic materials is of great significance for accelerating the research and application of NLC materials, especially in organic system.

Crystal structure of the Al8Cr5-type inter-metallic Al7.85Cr5.16.

An aluminium-deficient Al8Cr5-type inter-metallic with formula Al7.85Cr5.16 (octa-aluminium penta-chromium) was uncovered when high-pressure sinter-ing of a mixture with composition Al11Cr4 was carried out. Structure analysis reveals that there are three co-occupied positions with refined occupancy factors for Al atoms being 0.958, 0.772 and 1/2. The present phase is confirmed to be isotypic with the previously reported rhombohedral Al8Cr5 ordered phase [Bradley & Lu (1937). Z. Kristallogr. 96, 20-37] and structurally closely related to the disordered phases of rhombohedral Al16Cr9.5 and cubic Al8Cr5.

Crystal structure of Al2.95Cr0.59, a phase closely related to the η-phase in the binary Al-Cr system.

The monoclinic η-phase in the binary Al-Cr system was initially named by Bradley & Lu [Bradley & Lu (1937 ▸). J. Inst. Met. 60, 319-337] as having the composition Al11Cr2 (Al:Cr ratio = 5.5:1). Its crystal structure was later refined [Cao & Kuo (2008). J. Alloys Compd. 458, 30, 319-337] to have a slightly lower Al content (Al:Cr ratio = 5.16:1). In the present work, a monoclinic phase with composition Al2.95Cr0.59 (Al:Cr ratio = 5.04:1) was obtained by high-pressure sinter-ing (HPS) of a stoichiometric Al11Cr2 mixture. Structure analysis of this phase, hereafter named η', revealed a close relationship to the previously reported η-Al11Cr2 structure, but with different mixed-occupied sites. Five fully occupied sites exhibit refined site occupation factors of 0.899 (5), 0.984 (4), 0.977 (5), 0.946 (4) and 0.945 (4) for the corresponding Al atoms. Moreover, there are no split Al sites in the η'-structure as reported for the η-structure. The refined chemical composition of the η'-phase revealed that it comprises two Al atoms fewer and two Cr atoms more than the previously reported η-Al11Cr2 phase.

Liquid Exfibration and Optoelectronic Devices of Fibrous Phosphorus.

Quasi-one-dimensional (Q1D) semiconductor materials, such as carbon nanotubes, SbSI, MP15 (M = Li, Na, K), and selenium and tellurium nanowires, show amazing potential for applications in future nanoelectronic and optoelectronic devices. However, intricate chirality in the structure of carbon nanotubes limits their applications. Also, the performance of MP15 in optoelectronics has yet to be extensively explored. One new Q1D semiconductor material, fibrous phosphorus (FP), has recently received attention because its raw material is less toxic. However, the ability to characterize FP by phase identification is limited in the assessment of micro/nano-thickness, such as exfibrated FP. So, identifying a precise Raman spectrum will allow for much better characterization. Here, a sufficiently sharp Raman spectrum of FP was obtained and analyzed. Moreover, we demonstrated that high-quality, few-layer FP fibers with thicknesses as low as 5.55 nm can be produced by liquid-phase exfibration under ambient conditions in solvents. More importantly, an optoelectronic detector based on a single FP fiber field-effect-transistor configuration was investigated. A rise time as short as about 40 ms was obtained for the FP transistors, illustrating the potential of FP single bundle crystals as a new one-dimensional material for optoelectronic device applications.

First-principles investigation of novel polymorphs of Mg2C.

On the basis of the evolutionary methodology for crystal structure prediction, the potential crystal structures of magnesium carbide with a chemical composition of Mg2C are explored. Except the known cubic phase (Fm3̅m), two novel tetragonal structures (P42/mnm and I41/Amd) and two novel hexagonal structures (P63/mmc and P6̅M2) of Mg2C are found. All these four new phases are mechanically and dynamically stable by the calculated elastic constants and phonon dispersions. Furthermore, the effects of pressure and temperature on the phase transitions among different Mg2C polymorphs are investigated, implying that some new phases especially the P42/mnm phase may be synthesized in future. The ratio values of B/G are also calculated in order to analyze the brittle and ductile nature of these Mg2C phases. In addition, electronic structure calculations suggest that the I41/Amd phase is semimetallic and the other three new phases are all metallic, which is different from the previously proposed magnesium carbides. Meanwhile, the calculated electronic density maps reveal that strong ionic bonding exists between the Mg and C atoms.

Rich stoichiometries of stable Ca-Bi system: structure prediction and superconductivity.

Using a variable-composition ab initio evolutionary algorithm implemented in the USPEX code, we have performed a systematic search for stable compounds in the Ca-Bi system at different pressures. In addition to the well-known tI12-Ca2Bi and oS12-CaBi2, a few more structures were found by our calculations, among which phase transitions were also predicted in Ca2Bi (tI12 → oI12 → hP6), Ca3Bi2 (hP5 → mC20 → aP5) and CaBi (tI2 → tI8), as well as a new phase (Ca3Bi) with a cF4 structure. All the newly predicted structures can be both dynamically and thermodynamically stable with increasing pressure. The superconductive properties of cF4-CaBi3, tI2-CaBi and cF4-Ca3Bi were studied and the superconducting critical temperature Tc can be as high as 5.16, 2.27 and 5.25 K, respectively. Different superconductivity behaviors with pressure increasing have been observed by further investigations.

Novel metastable compounds in the Zr-B system: an ab initio evolutionary study.

Using ab initio evolutionary simulations, we have explored the potential crystal structures with up to 18 atoms in the unit cell for all possible stoichiometries of the Zr-B system. In addition to the reported ZrB, ZrB2, ZrB12, oP8-ZrB and Zr3B4, two extraordinary Zr2B3 and Zr3B2 have been found to be both mechanically and dynamically stable, as verified by the calculated elastic constants and phonon dispersions. The calculated formation enthalpies reveal that both the new phases may be synthesized and found in experiments. It also reveals that pressure is beneficial for the synthesis of all available phases, except for the ZrB phase. In addition, the values of the Vickers hardness for five Zr-B compounds are predicted utilizing two different models. Contrary to the known hard phases of ZrB2 and ZrB12, the two new compounds both have low values of hardness (less than 10 GPa), which is consistent with their excellent ductility deduced from the bulk and shear moduli. Electronic structure calculations suggest that the new phases are both metallic, while electronic density maps show strong ionic bonding characteristics between the Zr and B atoms. The crystal orbital Hamilton population (COHP) diagrams have also been calculated in order to further analyze the bonding features of the uncovered two novel phases.