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Wurtzite CuInS2 exhibits great potential for optoelectronic applications because of its excellent optical properties and good stability.

Superhard semiconductors have been long sought after for electronic device applications enduring extreme conditions, such as astronautics, due to their intrinsic toughness, high thermal and chemical stability. Here, we report the superhard p-type semiconductor Al2.69B50 single crystal with the determined Vickers hardness of ~ 40.5 GPa under the load of 0.49 N, being one of the hardest semiconductor compounds that have been ever found. With the direct band gap of 2.3 eV, Al2.69B50 exhibits excellent optical transmittance (> 90%,) covering the visible range from 459 nm to 760 nm and part of infrared range, and also shows high intensity of photon emission in the visible light. Al2.69B50 is very stable, thermally and chemically, with ultra-low density of ～2.52 g/cm3, allowing for further extension of its applications. Such an assembly of various excellent properties within one material has great implication for high power electronic design and applications.

Exploring the hydrophobicity of robust conductors is significant for electronic devices to simultaneously be used in a wet environment and extreme conditions. However, a combination of conductivity, strong mechanical properties, and hydrophobicity in one material is hindered by the inherent features of the materials. A new kind of robust hydrophobic conductor is designed in transition-metal diborides (TMdBs: TiB2, ZrB2, and HfB2) to break through this challenge. The results calculated by density functional theory indicate that high hardness comes from high shear and bulk modulus, which is consistent with experimental results (TiB2, 25.0 GPa; ZrB2, 17.5 GPa; HfB2, 21.5 GPa). The theoretical calculated results reveal that edge sides have a lower surface energy than basal plane (001) in TMdBs. Hence, the edge sides are exposed with a needle-like morphology in TMdBs. Moreover, needle-like surfaces exhibiting hydrophobicity have water contact angles of 132.0° (TiB2), 116.8° (ZrB2), and 114.0° (HfB2). The hydrophobicity arises from a lower surface free energy of edge sides in TMdBs and a rough surface that reduces the contact area of water and a solid. This work develops a new kind of robust functional material in TMdBs.

Improving the poor electrical conductivity of hard materials is important, as it will benefit their application. High-hardness metallic Mo2B was synthesized by high-pressure and high-temperature methods. Temperature-dependent resistivity measurements suggested that Mo2B has excellent metallic conductivity properties and is a weakly coupled superconductor with a T c of 6.0 K. The Vickers hardness of the metal-rich molybdenum semiboride reaches 16.5 GPa, exceeding the hardness of MoB and MoB2. The results showed that a proper boron concentration can improve the mechanical properties, not necessarily a high boron concentration. First-principles calculations revealed that the pinning effect of light elements is related to hardness. The high hardness of boron-pinned layered Mo2B demonstrated that the design of high-hardness conductive materials should be based on the structure formed by light elements rather than high-concentration light elements.

The high pressure structural changes of Cu3TeO6 have been investigated by using synchrotron radiation X-ray diffraction and Raman spectroscopy up to 23.2(4) and 45.9(7) GPa, respectively. It was fo...

Transition metal diborides (TMdBs

The combination of various desired physical properties greatly extends the applicability of materials. Magnetic materials are generally mechanically soft, yet the combination of high mechanical hardness and ferromagnetic properties is highly sought after. Here, we report the synthesis and characterization of nanocrystalline manganese boride, CrB-type MnB, using the high-pressure and high-temperature method in a large volume press. CrB-type MnB shares the specificity of large numbers of unpaired electrons of manganese ions and strong covalent boron zigzag chains. Thus, manganese mono-boride exhibits "strong" ferromagnetic, magnetocaloric behavior, and possesses high Vickers hardness. We demonstrate that zigzag boron chains in this structure not only play a pivotal role in strengthening mechanical properties but also tuning the exchange correlations between manganese atoms. Nontoxic and Earth-abundant CrB-type MnB is much more incompressible and tougher than traditional ferromagnetic materials. The unique combination of high mechanical hardness, magnetism, and electrical conductivity properties makes it a particularly promising candidate for a wide range of applications.

Under high pressure of 4 GPa, cooling at 10 °C/s from 1050 °C to ambient temperature induces unprecedented hardening by a factor of 4 (600 HV) in a binary Fe-15 wt.%Cr alloy that is traditionally unable to be hardened via heat treatment. A martensite of body centered cubic structure was induced, having the common features of hierarchical packet-block-lath structure of lath martensite in ferrous alloys, but with substructure of high density of twinned variants (lath) of 31 nm in average thickness. This study allows good combination of hardening and high temperature oxidation resistance in binary Fe-Cr system without alloying extra elements.

Obtaining both high hardness and toughness is a challenge in B4C-nano-adhesive composites. Solving the inhomogeneous distribution of nano-adhesives in B4C and forming the chemical bonding at grain ...

In virtue of mode tunability and inherent optical feedback, the lasing of semiconductor optical cavity has become the research focus of optoelectronic devices integrated on chip and optical systems...

The structural stability of Ti3AlC2 under high pressure is important for understanding its mechanical properties. Here, we conducted a high hydrostatic pressure synchrotron X-ray diffraction experiment and no structural phase transition was observed. Like most other MAX phases, Ti3AlC2 showed an anisotropic compression behavior. Most importantly, an anomaly in c/a ratio was observed at 20.3 GPa, indicating that a pressure-induced isostructural phase transition occurred here. Analysis of the electronic band structure and Fermi surface revealed that three bands crossed the Fermi surface under compression, which suggested that this isostructural phase transition can be considered to be motivated by an electronic topological transition. The subsequent Hall-effect measurements reconfirmed this variation of the electronic band at the Fermi surface, which can be regarded as the electronic origin for the observed isostructural phase transition. These results enrich the basic property data of Ti3AlC2 and would benefit the further understanding of this promising material.

Polycrystalline TiTa2O7 was synthesized directly by solid-state reaction methods. The structures were determined by using X-ray diffraction (XRD). The high-pressure Raman and UV-vis absorption spectra of TiTa2O7 were obtained up to 25 GPa in a diamond anvil cell (DAC) at room temperature. The Raman scattering results reveal that a pressure-induced amorphization occurs above 10.5 GPa. An inflection point was also observed at 11 GPa in the pressure-dependent bandgap energy spectra, which agrees well with the amorphization point found in Raman spectra. The temperature-dependent Raman and photoluminescence (PL) spectra of TiTa2O7 were also measured. The PL mechanism for TiTa2O7 was studied. It is worth noting that the Raman vibrations attributing to the bending vibration of the Ta (Ti)–O octahedron exhibit anomalous frequency shifts in both the high-pressure and temperature-dependent Raman spectra.

Two polymorphs of polycrystalline Ho2Ge2O7, one with tetragonal structure and the other with cubic structure, were synthesized by using different methods. The structural stabilities of these two polymorphs under high pressure were investigated by angle-dispersive X-ray diffraction (ADXRD). Pressure-induced amorphization was found in the tetragonal Ho2Ge2O7, which is suggested to be associated with the breaking-up of long chains of the edge-shared polyhedron group Ho4O20. By contrast, cubic Ho2Ge2O7 is stable at high pressures up to 33.3 GPa.

Magnetic materials attract great attention due to their fundamental importance and practical application. However, the relatively inferior mechanical properties of traditional magnetic materials limit their application in a harsh environment. In this work, we report an outstanding magnetic material that exhibits both fantastic mechanical and excellent magnetic properties, CuAl2-type Fe2B, synthesized by the high pressure and high temperature method. The magnetic saturation of Fe2B is 156.9 emu g-1 at room temperature and its Vickers hardness is 12.4 GPa which outclasses those of traditional magnetic materials. It exhibits good conductivity with a resistivity of 5.6 × 10-7 Ω m. Fe2B is a promising strong ferromagnetic material with high hardness, which makes it a good candidate for multifunction applications in a harsh environment. The high hardness of Fe2B originates from the Fe-B bond framework, and the strong ferromagnetism is mainly attributed to the large number of unpaired Fe 3d electrons. The competition of Fe 3d electrons to fall into Fe-B bonds or Fe-Fe bonds is the main factor for its magnetism and hardness. This work bridges the chasm between strong ferromagnetism and high hardness communities.

High boron content transition metal (TM) borides (HB-TMBs) have recently been regarded as the promising candidate for superhard multifunctional materials. High hardness stems from the covalent bond skeleton formed by high content of boron (B) atoms to resist deformation. High valence electron density of TM and special electronic structure from p-d hybridization of B and TM are the sources of multifunction. However, the reason of hardness variation in different HB-TMBs is still a puzzle because hardness is a complex property mainly associated with structures, chemical bonds, and mechanical anisotropy. Rich types of hybridization in B atoms (sp, sp2, sp3 ) generate abundant structures in HB-TMBs. Studying the intrinsic interaction of structures and hardness or multifunction is significant to search new functional superhard materials. In this review, the stable structure, hardness, and multifunctionality of HB-TMBs are summarized. It is concluded that the structures of HB-TMBs are mainly composed by sandwiched stacking of B and TM layers. The hardness of HB-TMBs shows a increasing tendency with the decreasing atom radius. The polyhedron in strong B skeleton provides hardness support for HB-TMBs, among which C2/m is the most possible structure to meet the superhard standard. The shear modulus (G 0) generates a positive effect for hardness of HB-TMBs, but the effect from bulk modulus (G 0) is complex. Importantly, materials with a value of B 0/G 0 less than 1.1 are more possible to achieve the superhard standard. As for the electronic properties, almost all TMB3 and TMB4 structures exhibit metallic properties, and their density of states near the Fermi level are derived from the d electrons of TM. The excellent electrical property of HB-TMBs with higher B ratio such as ZrB12 comes from the channels between B–B π-bond and TM-d orbitals. Some HB-TMBs also indicate superconductivity from special structures, most of them have stronger hybridization of d electrons from TM atoms than p electrons from B atoms near the Fermi level. This work is meaningful to further understand and uncover new functional superhard materials in HB-TMBs.

Superhard semiconductors have been long sought after for electronic device applications enduring extreme conditions, such as astronautics, due to their intrinsic toughness, high thermal and chemical stability. Here, we report the superhard p-type semiconductor Al

Regulating electron structure and electron–phonon coupling by means of pressure and temperature is an effective way to optimize thermoelectric properties. However, in situ testing of thermoelectric transport performance under pressure and temperature is hindered by technical constraints that obscure the intrinsic effects of pressure and temperature on thermoelectric properties. In the present study, a new reliable assembly was developed for testing the in situ thermoelectric transport performance of materials at high pressure and high temperature (HPHT). This reduces the influence of thermal effects on the test results and improves the success rate of in situ experiments at HPHT. The Seebeck coefficient and electrical resistivity of α-Cu2Se were measured under HPHT, and the former was found to increase with increasing pressure and temperature; for the latter, although an increase in the pressure acted to lower the electrical resistivity, an increase in the temperature acted to increase it. On increasing pressure from 0.8 to 3 GPa at 333 K, the optimal power factor of α-Cu2Se was increased by ∼76% from 2.36 × 10−4–4.15 × 10−4 W m−1 K−2, and the higher pressure meant that α-Cu2Se had its maximum power factor at lower temperature. The present work is particularly important for understanding the thermoelectric mechanism under HPHT.

The correlation between the crystal structure and the optoelectrical property of methylammonium lead iodide (MAPbI3) is investigated by measuring the optical absorption and the photoluminescence spectra of a microsized single-crystal MAPbI3 plate (MSCMP) up to 20.43 GPa with confocal μ-spectroscopy. The pressure-induced phase transitions of an MSCMP are identified by the absorption edges of the absorption spectrum and the fluorescence peaks of the PL spectrum. A tetragonal–cubic phase transition is confirmed under a pressure within the range of 0.23 to 0.46 GPa. The optical property of the cubic phase is dominated by the competition between Pb–I bond contraction and PbI6 octahedron tilt up to 2.72 GPa. Furthermore, the MAPbI3 plate experiences an isostructural cubic phase transition with a unique optical behavior below 3.90 GPa. Little amount of nonradiative high-pressure phase presents a radiative emission mixed with a radiative low-pressure phase, which originates from the diffusion and recombination of...

In this work, the lasing performance of a microsized single-crystal CsPbI3 triangular pyramid (MSCTP) is evaluated by measuring the lasing threshold at low temperature. The MSCTPs of well-defined facets are synthesized on a Si/SiO2 substrate with chemical vapor deposition. The MSCTP shows a spontaneous emission around 719 nm at room temperature and a stimulated emission resonant in a single Fabry-Perot mode within 148-223 K. The lasing threshold varies from 21.56 to 53.15 μJ/cm2 and presents a temperature dependence in an empirical exponential function with a characteristic temperature of 72.73 K. The temperature dependence of lasing behavior is ascribed to the competition between the exciton binding energy and thermal disturbance energy of CsPbI3. The results of this work provide us a perspective to engineer and optimize optoelectrical devices based on perovskite materials and a microsized optical cavity to investigate the light-matter interaction in quantum optics.

WB2-WB3-B4C composites were fabricated from powder mixtures of W and B13C2 by DC arc melting. XRD analysis illustrated that W has reacted with B13C2 and resulted in the formation of WB2-WB3-B4C composites. Vickers hardness of 55.7 ± 8.5 (load 0.49 N) and 34.2 ± 1.1 GPa (load 4.9 N) with corresponding Young's modulus of 575 GPa were observed for the as-synthesized composites. SEM and XPS results revealed that the composites consist of WB2, WB3, B4C, elemental boron and carbon. Raman spectra confirmed that B4C and carbon coexist in the composites. The harden mechanism of the as-synthesized composites including solid-solution hardening and dispersion hardening were analyzed in detail.

Chalcopyrite-structured semiconductor CuInSe2 has received considerable attention owing to its promising electrical and optical properties for nonlinear optical instruments and photovoltaic solar c...

BaTi0.7(Cu0.1Nb0.2)O3 ceramic was prepared using a solid-state method and its structure, valence states, conduction mechanism and dielectric properties were investigated in detail. A fine-grained microstructure and a distorted pseudo-cubic perovskite structure were confirmed by scanning electron microscopy, X-ray diffraction analysis and Raman spectroscopy. X-ray photoelectron spectroscopy analysis suggested that Cu in BaTi0.7(Cu0.1Nb0.2)O3 was polyvalent but the valence states of Ti and Nb were invariable. Mott's variable-range-hopping (VRH) conduction was observed. The two colossal dielectric constant plateaus in low- and high-temperature ranges were ascribed to the electrode and grain boundary responses, respectively. The VRH model described the low-temperature relaxation well, indicating that the dielectric relaxation was a polaron relaxation rather than Maxwell–Wagner type. Both grain and grain boundary resistances were well fitted by the VRH model, suggesting that the VRH mechanism was tenable in both grain and grain boundaries. The electron paramagnetic resonance signal was ascribed to Cu ions, and the linewidth showed a linear relationship with T−1/4, corresponding to the charge transfer between different valence via Cu+-O-Cu2+ and Cu2+-O-Cu3+ paths. The hopping of carriers was also responsible for the conduction and polaron dielectric relaxations.

SrTi1−3x(CuxNb2x)O3 (x = 0.05, 0.1, 0.15 and 0.2) ceramics were synthesized using a solid-state reaction method at 1400 °C in air. Their structures, valence states, conduction mechanisms and dielectric properties were investigated in detail. Fine grains and vibration modes of the samples related to the doping effects were observed. A distorted pseudo-cubic structure was confirmed by XRD and Raman spectroscopy. All ceramics exhibited a colossal dielectric constant and dielectric relaxations. The dielectric constant in the low- and high-frequency ranges for x = 0.05 and 0.1 was ascribed to the contribution of the grain boundary and grain, respectively, and the electrode polarization was significant at x = 0.15 and 0.2. The dielectric relaxation peaks obeyed the T−1/4 law at low temperature for all samples, confirming the polaron relaxation process. The electric modulus analysis confirmed that low-temperature dielectric relaxation was related to the grain response, and the electric conduction exhibited the same behavior with the dielectric relaxation. The variable-range-hopping conduction indicated a highly distorted structure and the localization of carriers in SrTi1−3x(CuxNb2x)O3, which was consistent with the XRD and Raman results. The mixed-valence structure of Cu was identified by XPS, and the polaron hopping between the mixed-valence Cu ions was supposed to be responsible for the dielectric relaxation and electric conduction.

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 B1 = 210.7 GPa of Fm-3m phase to B2 = 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.

Poor electrical conductivity severely limits the diverse applications of high hardness materials in situations where electrical conductivities are highly desired. A "covalent metal" TaB with metallic electrical conductivity and high hardness has been fabricated by a high pressure and high temperature method. The bulk modulus, 302.0(4.9) GPa, and Vickers hardness, 21.3 GPa, approaches and even exceeds that of traditional insulating hard materials. Meanwhile, temperature-dependent electrical resistivity measurements show that TaB possesses metallic conductivity that rivals some widely-used conductors, and it will transform into a superconductor at Tc =7.8 K. Contrary to common understanding, the hardness of TaB is higher than that of TaB2 , which indicates that low boron concentration borides could be mechanically better than the higher boron concentration counterparts. Compression behavior and first principles calculations denote that the high hardness is associated with the ultra-rigid covalent boron chain substructure. The hardness of TaB with different topologies of boron substructure shows that besides incorporating higher boron content, manipulating light element backbone configurations is also critical for higher hardness amongst transition metal borides with identical boron content.