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Ternary transition metal borides (TTMBs) will break materials application limitation in harsh service environments, owing to their structure versatility and high component tunable ability. Herein, we reported a solid solution boride CrFeB synthesized by high pressure and high temperature method. CrFeB yields an asymptotic hardness of 14.2 GPa and thermal stability temperature is up to 1250 K. DC magnetic susceptibility measurements revealed that there is a separation between zero-field cooled and field cooled curve at around 5 K, which indicated the spin glass behavior for CrFeB. Temperature dependence AC susceptibility analysis gives further evidence that the freezing temperature increases with frequency following Vogel-Fulcher law. On the basis of XPS results and first-principle calculations, we speculate that the complex magnetic behaviors may derive from the short-range magnetic exchange of same occupation sites two metal atoms. Cr and Fe atoms tend to have opposite magnetic moments in these short-range exchange behaviors. The intrinsic magnetic disorder and short-range frustration lead to spin random freezing of CrFeB at low temperatures, which conforms to typical spin glass characteristics. These results will contribute to understanding the complex magnetism behavior of CrFeB and provides a new idea to design multifunctional TTMBs. [Display omitted] • Novel ternary solid solution boride CrFeB was fabricated by high pressure and high temperature method. • CrFeB exhibits high hardness, excellent antioxidant capacity and spin-glass behavior at low temperature. • The short-range magnetic exchange and long-range random occupancy of two metals lead to the spin glass behavior for CrFeB. • Regulating the interactions between metal components will help optimize the performance of multicomponent metal borides. [ABSTRACT FROM AUTHOR]

Abstract The ab initio evolutionary algorithm is used to search for all thermodynamically stable ZnOS alloys at extreme pressure. Our calculations enable the discovery of a new stable structure at high pressure, namely, P 2 1 / m Zn 8 O 2 S 6 , as well as several metastable structures. We find that pressure can be used as an effective approach to forming stable ZnOS alloys. The variation in band gap of P 2 1 / m Zn 8 O 2 S 6 is calculated using a hybrid functional, which shows that P 2 1 / m Zn 8 O 2 S 6 initially increases and then decreases. We also believe that P 2 1 / m Zn 8 O 2 S 6 may be a potential material for increasing the efficiency of solar cells. Highlights • One stable structure (P 21/ m Zn8O2S6) and several metastable structures are discovered under high pressure. • Our results suggest that pressure can be used as an effective approach to form the stable ZnOS alloy. • The P 21/ m Zn8O2S6 may be a potential application material for increasing the efficiency of solar cells. [ABSTRACT FROM AUTHOR]

Abstract As a typical transition metal nitride and promising spintronic material, CrN has many controversial results because of crystallographic nitrogen defects. One is the bulk softening resulting from electrons transition from localized to itinerated. Hence, well crystalline CrN synthesized is extremely important to clear the structure behavior under pressure. Compressed experiments of well crystalline CrN synthesized were measured up to 30.2 GPa in DAC. Our results show a similar bulk modulus from B 1 = 210.7 GPa of Fm- 3 m phase to B 2 = 214.2 GPa of Pnma phase across the whole process of phase transition between 5.3 GPa–8.1 GPa. The X-ray photoemission spectra indicate no remarkable change of electron transferring between Cr and N and no difference of p-d hybridization across the phase transition. It is found that the softening of CrN does not take place during the phase transition despite of the change of the d spin correlation. However, compared to N vacancies that destabilize structure, the nitrogen atoms play a very important role in the magnetic material as magnetic interaction medium ligand atoms and in material elastic properties as well. This work is significant to further understand high pressure behavior of transition metal nitrides. Highlights • CrN of the least vacancies was synthesized by a new metathesis reaction under 5 GPa. • Compressed experiments confirm the close bulk moduli between two CrN phases. • XPS-T of two phases were performed and XPS of Pnma was first investigated. • Nitrogen vacancies cause lattice volume shrink and lower pressure transition point. [ABSTRACT FROM AUTHOR]

Boron-rich transition metal vanadium borides have excellent mechanical properties and are favorable potential candidates for fabricating superhard, multifunctional materials. Using first-principle methodology, two boron-rich vanadium borides, VB 3 with monoclinic C 2/ m and orthorhombic Amm 2 space groups, were found at ambient pressure and high pressure, respectively. The C 2/ m -VB 3 is composed of B 4 units and V 2 B 20 units while the Amm 2-VB 3 is comprised of a distorted VB 12 hexagonal prism. These two are sandwich-like structures of graphene-like boron sheets and transition metal vanadium atoms. The high-pressure Amm 2-VB 3 is preferable energetically to ambient-pressure C 2/ m -VB 3 at above 21.5 GPa and can be quenched to ambient pressure. The simulated Vickers hardness values of C 2/ m -VB 3 and Amm 2-VB 3 are 43.3 and 37.6 GPa at ambient pressure, respectively. The higher hardness of C 2/ m -VB 3 is attributed to the directional puckered hexagonal boron-boron network in its crystal structure. [ABSTRACT FROM AUTHOR]

The Mg 4 Nb 2 O 9 crystals grown by floating zone technology were used as prototypes to investigate optoelectronic parameters by measuring the absorption and transmittance spectra along the c -axis from 200 to 800 nm at room-temperature. The imaginary and real parts of the complex dielectric constants, extinction coefficient and refractive index for Mg 4 Nb 2 O 9 were obtained. The Cauchy–Sellmeier equation for Mg 4 Nb 2 O 9 was validated in the Urbach tail region (4.0–5.0 eV). The dispersion energy E d and oscillator energy E 0 were obtained via the single oscillator approximation. More interestingly, the self-trapped exciton and disorder of Mg 2+ and Nb 5+ between MgO 6 and NbO 6 octahedrons participating in the transition in the Urbach tail region were confirmed by the excitation spectrum. [ABSTRACT FROM AUTHOR]

ZnNb 2 O 6 single crystal grown via optical floating zone technology was selected as a prototype for optical phonon behavior investigation. Polarized Raman spectra were obtained in adequate parallel and crossed polarized configurations. All the obtained Raman modes were characterized for ZnNb 2 O 6 and were in good agreement with previous normal coordinate analysis. The selection rules for the columbite group were validated. The in-site temperature-dependent Raman spectra of columbite ZnNb 2 O 6 were also described, and the anharmonic interactions were discussed. [ABSTRACT FROM AUTHOR]

On the basis of the evolutionary methodology for crystal structure prediction, we have revealed a novel monoclinic C 2 /m structure TaB 4 with planar six-membered ring boron network along the crystallographic b axis. We name it as m -TaB 4 . The calculations of elastic constants and phonon dispersion confirm that m -TaB 4 is mechanical and dynamical stable. Further calculations predicate that this structure is an ultrahard material with a large hardness (29 GPa). The presence of strong covalent boron–boron bonds and planar six-membered ring boron network in m -TaB 4 are crucial for its high hardness. [ABSTRACT FROM AUTHOR]

• Polycrystalline β -FeB sample with zigzag boron chains substructure was fabricated by high pressure and high temperature. • β -FeB exhibits high saturation magnetization, good antioxidant capacity, high hardness and low resistivity. • Majority spin state electrons are the main participants in electrons transfer and bonding between Fe and zigzag boron chains. • Spin-selective electrons transfer effect in TMBs can effectively modulate the hardness, magnetism and conductivity. Complex boron substructures lead to diversity properties for transition metal borides (TMBs), that provides them many application possibilities in numerous fields. To clarify the actual effect of boron substructures on mechanical, magnetic and electrical properties, we prepared polycrystalline β -FeB samples with zigzag boron chains by high pressure and high temperature. β -FeB exhibits high saturation magnetization (79.54 emu/g), good antioxidant capacity (> 800 K), high hardness (15.62 GPa) and low resistivity (3.4 × 10−6 Ω m); thus, it is a promising magnetic material for extreme environmental applications. Subsequently, we performed first-principle calculations combined with X-ray photoelectron spectroscopy analysis and found that the free electrons transferred from Fe atoms stabilize the zigzag boron chains. Spin selection occurs during electron transfer and bonding, with majority spin state electrons as the main participants. The zigzag boron chain substructure provides excellent mechanical properties, at the expense of electrical and magnetic properties. Therefore, we speculate that the spin-selective electrons transfer between the metal and boron substructure can effectively modulate the electrical, mechanical, and magnetic properties of TMBs. This study introduces an effective route for the design, preparation, and applications of high-hardness multifunctional TMBs. [ABSTRACT FROM AUTHOR]

• Synthesis of polycrystalline Mo 2 C specimens has been carried out firstly under high pressure and high temperature. • Mo 2 C presents superconductivity below 7.5 K and the hardness is far higher than the traditional superconductive materials. • Covalent [Mo6C] octahedral unit related to good conductivity and high hardness. • Mo 2 C is a hard superconductor to bridging the gap between high hardness and superconductivity communities. [Display omitted] Hard superconducting materials are of particular interest for electromechanical applications under high strain and stress. In this work, Mo 2 C was synthesized using high temperature and high pressure (HPHT) methods. In view of characterizations, Mo 2 C transforms into a superconductivity state below the temperature of 7.5 K and the asymptotic Vickers hardness is about 13.4 GPa. Its hardness is compatible with that of commonly used hard alloys, which is a potential hard superconducting material. Based on the results of our first-principle calculations, superconductivity and hardness come from the high density of states at the Fermi energy level and high hardness originates from the strong hybridization between Mo-4 d orbitals and C-2 p orbitals. By introducing the light element C atoms into the transition metal Mo to form a 'covalent metal' structure, the hardness and mechanical properties of the superconducting material can be improved which gives a way to design hard superconducting materials. [ABSTRACT FROM AUTHOR]

Abstract: Platinum boride (PtB) nanowires have been successfully fabricated with direct current arc discharge method using a milled mixture of platinum (Pt) and boron nitride (BN) powders. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the compositions, morphology, and structures of the samples. The results show that PtB nanowires are 30–50nm thick and 20–30μm long. TEM and selected area electron diffraction (SAED) patterns identify that the PtB nanowires are single-crystalline in nature. A growth mechanism based on vapor–liquid–solid (VLS) process is proposed for the formation of nanowires. [Copyright &y& Elsevier]

Abstract: CeO2 nanosheets with (110) dominated surface were synthesized for the first time by a facile one-step hydrothermal method without the assistance of any surfactant or template. The role of NH3·H2O on tailoring the morphology of CeO2 nanocrystals was investigated. It was found the NH3·H2O not only serves as the precipitant, but also acts as structural direction agent in the formation of (110)-dominated CeO2 nanosheets. Raman and XRD spectra showed that the sample has a cubic fluorite structure. Compared with bulk CeO2 materials, the prepared CeO2 nanosheets exhibit an obvious blue-shift in UV absorbance. The increase of the direct band gap energy of the obtained sample exceeds 8%. This method provides an environmentally friendly way for preparing CeO2 nanostructures and tailoring their morphology. It may also be extended to the synthesis of other nanomaterials. [Copyright &y& Elsevier]

Abstract: Monodisperse CeO2 nanospheres with the average size of 40nm, self-assembled by well-crystalline CeO2 ultrafine nanoparticles were synthesized through a facile solvothermal route using n-butanol as solvent in the absence of any surfactant or template. The formation process of the monodisperse self-assembly CeO2 nanospheres is briefly discussed. The key function of n-butanol is investigated by comparative experiments. It is found that n-butanol not only serves as solvent, but also acts as surfactant in the formation of monodisperse self-assembly CeO2 nanospheres. Raman and XRD spectra show that the sample is pure cubic fluorite type of structure. Compared to the bulky CeO2 materials, the prepared CeO2 nanospheres exhibited an obvious blue-shifting in UV absorbance. The direct band gap energy of the obtained sample increases by exceeding 10%. Our study provides an effective approach to control CeO2 morphology which has potential application in synthesis of other nanomaterials. [Copyright &y& Elsevier]

Abstract: Nanoporous anatase TiO2 rods and rutile TiO2 chrysanthemums were successfully synthesized via a simple ethylene glycol-mediated synthesis route. Their morphologies, phase compositions and components were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman and IR, respectively. The results show that a self-assembly growth takes place in the calcination under vacuum, which makes the titanium glycolate rods transform into rutile TiO2/C chrysanthemums rather than anatase TiO2 rods. It also indicates that the carbon plays an important role in the phase transition process which promotes the phase transition to rutile TiO2 at a lower temperature (400°C). It provides a new approach to prepare nanoporous rutile TiO2 nanomaterials under low temperature. [Copyright &y& Elsevier]