Obtaining room-temperature superconductors has long been a research hotspot in the field of condensed matter physics. Previous studies have shown that doping strategies can effectively enhance the superconducting properties of materials. In this work, we employed first-principles calculations combined with the particle swarm optimization method to explore the structural possibilities of the Ca-doped As-H ternary system and to calculate the electronic and superconducting properties of the newly identified structures. Two thermodynamically stable hydrides were found under high pressure. The $P$4/nmm-Ca$_{2}$AsH$_{4}$ phase remains thermodynamically stable within the pressure range of 90-200 GPa, while the Cc-Ca$_{2}$AsH$_{6}$ phase exhibits stability over a broader range of 79-200 GPa. Electron-phonon coupling analysis indicates that the superconducting critical temperatures ($T_{\rm c}$) of $P$4/nmm-Ca$_{2}$AsH$_{4}$ and Cc-Ca$_{2}$AsH$_{6}$ are 11 K and 16 K at 100 GPa, respectively. The incorporation of Ca significantly reduces the thermodynamic stability pressure of As-H compounds with higher hydrogen content, thereby improving their synthetic accessibility.

LiFePO$_{4}$ has normal olivine-structured ($\alpha $-LFP) and high pressure ($\beta $-LFP) phases, with the former being one of the cathode materials for commercial Li-ion batteries. Despite extensive focus on the respective electrochemical properties of the two phases, there is a lack of comparative studies on their electronic and magnetic properties, and the origin of the structural phase transition remains unclear. By combining first-principles calculations with molecular dynamics simulations, we find that the anisotropic compression of Li-O bonds drives the structural phase transition from $\alpha $-LFP to $\beta $-LFP at a critical pressure of 20 GPa, while $\beta $-LFP undergoes a transition from semiconductor to metal due to Fe$^{3+}$ generated during delithiation. Their antiferromagnetic (AFM) ground states are predicted to arise from the negative magnetic exchange interactions between nearest and next-nearest neighbor sites, with the corresponding Néel temperature showing significant enhancement under pressure. Furthermore, compared with $\alpha $-LFP, $\beta $-LFP shows increases in bulk, shear, and Young's moduli of 8%, 13%, and 12%, respectively. These findings enrich the physical property data of LiFePO$_{4}$ phase compounds, providing knowledge for expanding the application scenarios of the $\alpha $-LFP phase under special operating conditions such as high pressure.

To enhance boron doping efficiency and reduce metal impurities in diamonds, selecting an appropriate metal solvent is essential for producing p-type diamonds using the high-pressure high-temperature (HPHT) method. This paper presents a detailed study of the properties and characteristics of boron-doped diamond (BDD) single crystals grown using FeNi and FeCo solvents through the HPHT method. The results indicate that, with the same TiB$_{2}$ addition ratio, BDD crystals grown using FeCo solvent have a higher concentration of uncompensated boron ions, resulting in improved boron doping efficiency. Additionally, by growing BDD in the same synthesis environment (FeCo-3 wt% TiB$_{2})$ using (111) and (100) seed crystals as growth surfaces, it was found that the boron content in the crystal grown from the (100) seed crystal was higher than that in the crystal grown from the (111) seed crystal. Additionally, the crystals grown with the FeCo solvent contained fewer metal elements (Fe and Co) compared to those produced with the FeNi solvent (Fe and Ni), which supported the growth of high-quality BDD single crystals. This indicated that the choice of growth planes significantly influences the incorporation of boron in diamonds. Our findings hold significant research value for the development of high-quality p-type diamond semiconductors using the HPHT method.

Using first-principles evolutionary crystal structure prediction, we systematically investigate scandium polychlorides across 50-300 GPa, predicting multiple thermodynamically stable phases ScCl, ScCl$_{2}$, ScCl$_{3}$, ScCl$_{5}$, and ScCl$_{7}$ with unconventional stoichiometries. The exceptional stability of these compounds stems from the mutually compatible crystal orbitals of the Sc and Cl sublattices, strong ionic interactions, and the formation of Cl-Cl homobonds. These factors play critical roles in stabilizing scandium chloride compounds with various unconventional stoichiometries. Notably high-pressure novel ScCl phases with $P$6$_{3}$/mmc and Pm-3$m$ symmetries can be metastable at ambient pressure upon decompression and convert into superconductive electrides. Pm-3-ScCl$_{7}$ exhibits significant pressure-modulated superconductivity, featuring an enhancement of $T_{\rm c}$ to 10.91 K at a low pressure of 75 GPa. In addition, the universal superconductivity found in the Pm-3 structured chlorides suggests a promising structural prototype for pressure-tunable superconductors.

Nickel-based superconductors have attracted great attention due to the finding of the Ruddlesden-Popper (R-P) bilayer nickelate La$_{3}$Ni$_{2}$O$_{7}$ with superconducting critical temperature ($T_{\rm c}$) of 80 K at pressure above 14 GPa. Recent efforts have been devoted to the study of La$_{2}$PrNi$_{2}$O$_{7}$, while the detailed structure remains unclear. In this work, we explore the stability and physical properties of such an interesting system by using density functional theory and the $U$ parameter simulation method implemented in VASP. The results show that the enthalpy of La$_{2}$PrNi$_{2}$O$_{7}$ is slightly larger than its parent material bilayer R-P nickelate La$_{3}$Ni$_{2}$O$_{7}$. The electronic structure analysis indicates that near the Fermi level, the e$_{\rm g}$ orbit of Ni dominates and strongly hybridizes with the 2p orbit of O, thereby forming a significant van Hove singularity that is conducive to superconductivity. The Amam phase to the $I4/mmm$ phase occurs, accompanied by an increase in the bandwidth of Ni 3d$_{z^{2}}$ and an enhancement of the bonding-antibonding splitting (from about 0.5 eV to 1.5 eV), which leads to an increase in the density of states at the Fermi level. Our findings provide insights into the preparation and superconductivity of R-P bilayer nickelate.

Electrides, characterized by spatially confined anionic electrons, have emerged as a promising class of materials for catalysis, magnetism, and superconductivity. However, transition-metal-based electrides with diverse electron dimensionalities remain largely unexplored. Here, we perform a comprehensive first-principles investigation of Y-Co electrides, focusing on Y$_{3}$Co, Y$_{3}$Co$_{2}$, and YCo. Our calculations reveal a striking dimensional evolution of anionic electrons: from two-dimensional (2D) confinement in YCo to one-dimensional (1D) in Y$_{3}$Co$_{2}$ and zero-dimensional (0D) in Y$_{3}$Co. Remarkably, the YCo monolayer exhibits intrinsic ferromagnetism, with a magnetic moment of 0.65 $\mu_{\rm B}$ per formula unit arising from spin-polarized anionic electrons mediating long-range coupling between Y and Co ions. The monolayer also shows a low exfoliation energy (1.66 J/m$^{2}$), indicating experimental feasibility. All three electrides exhibit low work functions (2.76 eV-3.11 eV) along with Co-centered anionic states. This work expands the family of transition-metal-based electrides and highlights dimensionality engineering as a powerful strategy for tuning electronic and magnetic properties.

Quasi one-dimensional polycrystalline samples of Ba$_{3}$Hf(Se$_{1-x}$Te$_{x}$)$_{5}$ ($x = 0$-1) are synthesized under high-temperature and high-pressure conditions. Using the powder x-ray diffraction technique and first-principles calculations, Ba$_{3}$HfSe$_{5}$ is identified as having a hexagonal structure with a space group of $P$6$_{3}$/mcm (193) and lattice constants of $a = 9.5756(1) $ Å, $c =6.3802(7) $ Å. The structure is composed of Hf(Se$_{1}$)$_{6}$ chains and Se$_{2}$ linear chains extending along the $c$-axis. As the doping content of Te increases, the lattice expands and leads to 5.8% and 7.3% increases of the $a$ and $c$ values and a 20.1% increase of the unit cell volume of Ba$_{3}$HfTe$_{5}$ compared to Ba$_{3}$HfSe$_{5}$. The detailed structural refinements show that the Hf vacancies decrease gradually as Te doping increases in the Ba$_{3}$Hf(Se$_{1-x}$Te$_{x}$)$_{5}$ ($x = 0$-1) materials, which leads to a decrease of electronic localization. In addition, the lower electronegativity of Te and the more extended orbitals with respect to Se contribute to orbital overlap between the inter chains. All these dominate the enhanced electron hopping, leading to a reduction of the bandgap from 1.95 eV to 0.23 eV for Ba$_{3}$Hf(Se$_{1-x}$Te$_{x}$)$_{5}$ ($x = 0$-1) materials as the Ba$_{3}$HfSe$_{5}$ evolves to Ba$_{3}$HfTe$_{5}$.

The particle swarm optimization algorithm has predicted a series of binary cadmium hydrides that could be dynamically stable at pressures between 100 GPa and 300 GPa. These low-energy phases are composed of both Cd atoms and H$_{2}$ molecules. Here, we propose a hitherto unknown metastable Cmcm-CdH$_{6}$ phase, consisting of one-dimensional zigzag graphite-like hydrogenic H$_{6}$ chains, quasimolecular H$_{2}$ units and Cd atoms, which is metallic above 290 GPa. Due to H$_{2} \sigma \to {\rm Cd}$ d donation and Cd $\rm d \to H_{2} \sigma^{\ast } $ back-donation, the electrons occupy antibonding orbitals for both types of hydrogen atoms. This results in weakened chemical bonds in the Cmcm-CdH$_{6}$ phase via a Kubas-like mechanism, promoting the emergence of high superconductivity, which is estimated to be up to $\sim 60 $ K at 290 GPa. This work will inspire the search for superconductivity in materials based on group IIB hydrides under pressure.

Two-dimensional tellurium (2D-Te) exhibits strong spin-orbit coupling and a chiral structure. Studying its magnetotransport properties is crucial for the development of spintronic technologies and the exploration of novel device applications. The magnetotransport properties of 2D-Te under varying temperatures and high pressures warrant further study. In this paper, the magnetotransport behavior of 2D-Te under low-temperature and high-pressure conditions is investigated. At room temperature, the magnetoresistance (${\rm MR}$) increases with increasing magnetic field, exhibiting positive ${\rm MR}$ behavior below 4.3 GPa. During decompression, ${\rm MR}$ is almost constant with decreasing pressure. ${\rm MR}$ is more sensitive to pressure at lower temperatures.

The ground-state magnetic ordering of uranium mononitride (UN) remains a contentious topic due to the unexpected lack of crystallographic distortion in the traditionally accepted $1\bm{k}$ antiferromagnetic (AFM) state. This discrepancy casts doubt on the validity of the $1\bm{k}$ magnetic ordering of UN. Here, we investigate the crystal structure, high-pressure phase transitions, and dynamical and mechanical properties of UN in its $1\bm{k}$ and $3\bm{k}$ AFM ground states using density functional theory (DFT). Our results reveal that the undistorted $3\bm{k}$ AFM state of Fm$\overline{3}$m within the ${\rm DFT}+{U}+{\rm SOC}$ scheme is more consistent with experimental results. The Hubbard U and spin-orbit coupling (SOC) are critical for accurately capturing the crystal structure, high-pressure structural phase transition, and dynamical properties of UN. In addition, we have identified a new high-pressure magnetic phase transition from the nonmagnetic (NM) phase of R$\overline{3}$m to the P$6_{3}$/mmc AFM state. Electronic structure analysis reveals that the magnetic ordering in the ground state is primarily linked to variations in partial 5f orbital distributions. Our calculations provide valuable theoretical insights into the complex magnetic structures of a typical strongly correlated uranium-based compound. Moreover, they provide a framework for understanding other similar actinide systems.

Tin sulfide (SnS) is a promising non-toxic thermoelectric (TE) material to replace SnSe (Se is toxic), due to its similar structure and low thermal conductivity ($\kappa$) comparable to SnSe. However, the poor electrical conductivity ($\sigma$) of SnS results in lower TE performance. In this work, high pressure was utilized to regulate the electronic structure, thereby mediating the conflict of electron and phonon transport to optimize the TE performance. In situ measurements of thermoelectric properties for SnS under high pressure and high temperature revealed that although the Seebeck coefficient ($S$) and $\kappa$ slightly decrease with increasing pressure, the $\sigma$ dramatically increases with increasing pressure, finally increasing the dimensionless figure of merit ($ZT$). The $\sigma $ increases from 2135 S$\cdot$m$^{-1}$ to 83549 S$\cdot$m$^{-1}$ as the pressure increases from 1 GPa to 5 GPa at 325 K, representing an increase of an order of magnitude. The high $\sigma $ of SnS leads to an increase in the $PF$ to 1436 μW$\cdot$m$^{-1}\cdot$K$^{-2}$ at 5 GPa and 652 K. The maximum $ZT$ value of 0.77 at 5 GPa and 652 K was obtained, which is 4 times the maximum $ZT$ under ambient pressure and is comparable to that of doped SnS. The increase in $\sigma$ is due to the fact that pressure modulates the band structure of SnS by narrowing the band gap from 1.013 eV to 0.712 eV. This study presents a valuable guide for searching new high TE performance materials using high pressure.

The emergence of high-temperature superconductivity in hydrogen-rich compounds has opened up promising avenues for investigating unique hydrogen motifs that exhibit exceptional superconducting properties. Nevertheless, the requirement for extremely high synthesis pressures poses significant barriers to experimentally probing potential physical properties. Here, we have designed a structure wherein NH$_{3}$ tetrahedra are intercalated into the body-centered cubic lattice of Yb, resulting in the formation of Yb(NH$_{3}$)$_{4}$. Our first-principles calculations reveal that metallic behavior emerges from the ionization of sp$^{3}$-hybridized $\sigma$-bonds in NH$_{3}$, which is enabled by electron transfer from ytterbium orbitals to NH$_{3}$ anti-bonding $\sigma$-orbitals. A distinctive feature of this structure is the Fermi surface nesting, which leads to optical phonon softening and consequently enhances electron-phonon coupling. The subsequent density-functional theory (DFT) calculations demonstrate that this $I$-43$m$ phase of Yb(NH$_{3}$)$_{4}$ exhibits a superconducting critical temperature ($T_{\rm c}$) of 17.32 K under a modest pressure of 10 GPa. Our investigation presents perspectives on achieving phonon-mediated superconductivity at relatively low pressures, thereby opening up extensive possibilities for the attainment of high-temperature superconductivity in hydrogen-based superconducting systems with specific ionized molecular groups.

High pressure can alter the properties of matter and modulate the excited-state relaxation behavior of materials without chemical intervention. In this study, high pressure was combined with steady-state absorption and fluorescence spectroscopy, as well as transient spectroscopy techniques, to investigate its effect on the optical properties of the stimuli-responsive material (2Z,2$'$Z)-2,2$'$-(1,4-phenylene)bis(3-(4-(9H-carbazol-9-yl)phenyl)acrylonitrile) (CzCNDSB). With increasing pressure, the steady-state absorption and fluorescence peaks of CzCNDSB crystals exhibit red shifts, which are fully reversible. At the same time, pressure causes the molecules to pack more closely, leading to an increase in both the number and energy of multiplet self-trapped state, while the energy of local excited state decreases. The steady-state and transient results provide information on electronic energy levels, excited-state dynamics, and other properties of CzCNDSB, which show strong pressure dependence. These findings highlight the potential of CzCNDSB for practical applications such as photodetectors and solar energy conversion.

Metal superhydride compounds (MSHCs) have attracted much attention in the fields of high-pressure physics due to the superconductivity properties deriving from the metallic-hydrogen-like characteristics and relatively mild synthesis conditions. However, their energetic performance and related potential applications are still open issues till now. In this study, CaH$_{6}$ and NbH$_{3}$, which exhibit evidently differences in their geometric and electronic structures, were chosen as examples of MSHCs to investigate their energetic performance. The structure, bonding features and energetic performance of CaH$_{6}$ and NbH$_{3}$ were predicted based on first-principles calculations. Our results reveal that high-pressure MSHCs always exhibit high energy densities. The range of theoretical energy density of CaH$_{6}$ was predicted as 2.3-5.3 times of TNT, while the value for NbH$_{3}$ was predicted as 1.2 times of TNT. Our study further uncover that CaH$_{6}$ has outstanding energetic properties, which are ascribed to the three-dimensional (3D) aromatic H sublattice and the strong covalent bonding between the H atoms. Moreover, the detonation process and products of rapid energy-release stage of CaH$_{6}$ were simulated via AIMD method, based on which its superior combustion performance was predicted and its specific impulse was calculated as 490.66 s. This study not only enhances the chemical understanding of MSHCs, but also extends the paradigm of traditional energetic materials and provides a new route to design novel high energy density materials.

Quasi-one-dimensional systems provide a unique platform for the exploration of novel quantum states due to their enhanced electronic correlations, strong anisotropy, and dimensional confinement. Among various external tuning methods, physical pressure has been experimentally demonstrated to be an exceptionally potent and precise method for modulating both the structural and electronic properties of quasi-one-dimensional systems. In this review, we focus on the application of pressure to construct pressure-temperature phase diagrams of quasi-one-dimensional materials and explore the intricate relationships among quantum phenomena between superconductivity and other electronic states, such as charge density wave, topological quantum states, and antiferromagnetism. By analyzing representative examples across distinct material families, we demonstrate how pressure can be used not only to induce superconductivity but also to reveal underlying quantum critical points and drive topological phase transitions. We emphasize the significant potential of pressure as a crucial tuning parameter for revealing novel quantum phenomena and driving the progress in advanced low-dimensional quantum materials.

MgO is one of the most abundant minerals in the Earth's interior, and its structure and properties at high temperature and pressure are important for us to understand the composition and behavior in the deep Earth. In the present work, first-principles molecular dynamics calculations were performed to investigate the pressure-induced structural evolution of the MgO melts at 4000 K and 5000 K. The results predicted the liquid-solid phase boundaries, and the calculated viscosities of the melts may help us to understand the transport behavior under the corresponding Earth conditions.

The recently discovered mixed-valence compound Eu$_{9}$MgS$_{2}$B$_{20}$O$_{41}$ is composed of triple-kagomé-layers separated by nonmagnetic Mg$^{2+}$ ions, and intervalence charge transfer has been observed in the mixed Eu$^{2+}$ and Eu$^{3+}$ ions within the kagomé layers, exhibiting similar characteristics typical of a quantum spin liquid. In this study, high-pressure in situ x-ray diffraction measurements on Eu$_{9}$MgS$_{2}$B$_{20}$O$_{41}$ were conducted within the range of 0.1 MPa to 64.4 GPa. The results revealed that the stabilization of the ambient-pressure phase, with no transition from mixed valence to single valence observed within the studied pressure range. The bulk modulus of the sample was determined to be 167.3(28) GPa and 180.8(17) GPa, for the single-crystal and powder x-ray diffraction data at room temperature, respectively. These values correspond to approximately 40% of the bulk modulus of diamond. Moreover, absorption spectroscopy measurements were carried out up to 37.9 GPa, revealing a $\sim 20$% reduction in the energy band gap, mainly due to the shortened Eu-O bond lengths. The relationship between pressure and band gap demonstrates a nearly linear trend, with a slope of $-0.013$ eV/GPa. The findings of the present study imply that the studied sample demonstrates considerable robustness under extreme pressures.

The properties and creation of optical centers in diamond are essential for applications in quantum technology. Here, we study the photoluminescence (PL) spectroscopy behavior at low temperatures of diamond subjected to electron irradiation and annealing heat treatment. Through temperature variation testing, it was found that the NV$^{-}$ center intensity of diamond with a nitrogen content of 150 ppm before treatment is insensitive to the experimental temperature, but significantly increases with decreasing temperature after treatment, showing sensitivity to temperature. In addition, the H3 center also shows an increasing trend with decreasing temperature. The results of annealing diamond with a nitrogen content of 730 ppm showed that even at a low temperature of 93 K, no NV$^{-}$ centers were detected, but there were a large number of Ni-N related centers, especially NE8 centers. Our findings can promote a deeper understanding of the behavioral characteristics of HPHT-diamond optical centers in low-temperature environments.

Electrically conductive carbide ceramics with high hardness and fracture toughness are promising for advanced applications. However, enhancing both electrical conductivity and fracture toughness simultaneous is challenging. This study reports the synthesis of (Ti$_{0.2}$W$_{0.2}$Ta$_{0.2}$Hf$_{0.2}$Mo$_{0.2}$)C-diamond composites with varying densities using high-pressure and high-temperature (HPHT) method. The carbides are uniformly dispersed in a titanium carbide matrix, forming conductive channels that reduce resistivity to 4.6$\times10^{-7}$ $\Omega $$\cdot$m. These composite materials exhibit metallic conductivity with a superconducting transition at 8.5 K. Superconducting behavior may result from d-p orbital hybridization and electron-phonon coupling in transition metal carbides, such as TaC, Mo$_{2}$C, and MoC. Optimizing intergranular bonding improves the fracture toughness without compromising hardness. The highest indentation toughness value is $10.1 \pm 0.4 $ MPa$\cdot$m$^{1/2}$, a 130% increase compare to pure TiC. Enhanced toughness arises from transgranular and intergranular fracture modes, multiple crack bridging, and large-angle crack deflection, which dissipate fracture energy and inhibit crack propagation. This study introduces a novel microstructure engineering strategy for carbide ceramics to achieve superior mechanical and electrical properties.

Continuously improving the mechanical properties of ultra-high-temperature ceramics (UHTCs) is a key requirement for their future applications. However, the mechanical properties of conventional UHTCs, HfB$_{2}$ and ZrB$_{2}$, remain unsatisfactory among transition metal light-element (TMLE) compounds. TiB$_{2}$ has superior mechanical properties compared to both HfB$_{2}$ and ZrB$_{2}$, but suffers from inherent brittleness and limited oxidation resistance. In this work, low-content solid-solution strengthening was used to fabricate dense samples of Ti$_{x}$(Hf/Zr)$_{1-x}$B$_{2}$ (THZ) under high pressure and high temperature (HPHT). Compared to pure TiB$_{2}$, Ti$_{0.94}$(Hf/Zr)$_{0.06}$B$_{2}$ exhibits a significant 38.8% increase in oxidation resistance temperature (950 $^\circ$C), while Ti$_{0.91}$(Hf/Zr)$_{0.09}$B$_{2}$ shows a notable 28% enhancement in fracture toughness (5.8 MPa$\cdot$m$^{1/2}$). The synergistic effect of a dual-atom solid-solution results in local internal stress and anomalous lattice contraction. This lattice contraction helps resist oxygen invasion, thereby elevating the oxidation resistance threshold. Additionally, the internal stress induces crack deflection within individual grains, enhancing toughness through energy dissipation. This work provides a new strategy for fabricating robust UHTCs within TMLE systems, demonstrating significant potential for future high-temperature applications.