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Mn2(C2H6N6)4(NO3)4·2H2O (Mn) as one of the energetic coordination complexes was chosen for high‐pressure research. In this work, Mn was analyzed by in situ Raman scattering, infrared absorption, and synchrotron angle‐dispersive X‐ray diffraction (ADXRD) technologies up to ~20 GPa at room temperature. The vibrational modes of Mn at ambient pressure were comprehensively resolved based on the experimental results. Detailed spectral analyses revealed that Mn underwent three pressure‐induced phase transitions at 0.5, 2.5, and 5.7 GPa, respectively. ADXRD experiments confirmed the existence of these three phase transitions in Raman and infrared spectra analyses. Based on the analysis of the vibrational spectra and the changes of lattice parameters under pressure, it can be considered that the deformation of the 3‐hydrazino‐4‐amino‐1, 2, 4‐triazole (HATr) ligand led to the first phase transition, and the distortion of the triazole ring induced the second phase transition, and the rearrangement of the hydrogen bonds resulted in the third phase transition. In addition, it can be inferred from Raman spectra and ADXRD data that Mn may have experienced the abnormal expansion during the first phase transition. This work may lay the foundation for further investigating the structure and properties of energetic coordination complexes under pressure. [ABSTRACT FROM AUTHOR]

Red-emitting CaMoO 4 :Eu3+ nanosheets were prepared via a facile precipitation method at room temperature without any organic additives. The structural characterization indicates that these nanosheets are single-crystalline with an average diameter of ∼1.657 μm and a thickness of ∼10 nm. We investigated the high-pressure behaviors of bulk CaMoO 4 and CaMoO 4 :Eu3+ nanosheets by in situ high-pressure synchrotron angle-dispersive X-ray diffraction (XRD) technique at room temperature with the pressures up to 35.0 and 40.1 GPa, respectively. Two pressure-induced phase transitions were observed for both bulk CaMoO 4 and CaMoO 4 :Eu3+ nanosheets in the range of studied pressure. The two high-pressure phases were analyzed and identified to be monoclinic structures with I 2/a and P 2 1 /n space group, respectively. The compressibility of the CaMoO 4 is highly non-isotropic, and the c -axis is more compressible than a -axis and b -axis. Furthermore, the compressibility of the c -axis of CaMoO 4 :Eu3+ nanosheets is greater than that of bulk CaMoO 4. On the release of pressure from 35.0 to 40.1 GPa, the initial phase is recovered, implying that the observed structural modifications are reversible. CaMoO 4 : Eu3+ sheets also show higher luminescence efficiency that of bulk CaMoO 4 : Eu3+, which is reflected in higher Ω 2 value. The continuous shift of emission peaks indicates the changes in local symmetry of Eu3+ with pressure, which is consistent with our high-pressure XRD study. The potential applications of CaMoO 4 :Eu3+ nanosheets were explored and our findings show that white light with excellent color quality (CRI>90) and a high LER up to 345 lm/W could be achieved. • The second phase transition of CaMoO 4 is proposed. • The structure of the second high-pressure phase is predicted. • The luminescent efficiency of the CaMoO 4 :Eu3+ nanosheets is higher that of bulk counterpart based on J-O calculation. • The novel white LED device structure is designed based on CaMoO 4 :Eu3+ nanosheets and metal halide perovskites. [ABSTRACT FROM AUTHOR]

Polynitrides have excellent physical and chemical properties as well as have drawn wide attention. Through the first-principles calculations and CALYPSO structure searching approach, we calculated the overall structure of YN components (from 0.5 to 10) and established the pressure versus composition diagram and pressure versus structure phase diagram of the YN system. This paper focuses on the YN 2 structure (space group P 2 1) which can be stable at 0 GPa and the YN 10 structure with the highest nitrogen content (space group Imm2) with the intriguing chain-like N 10 cage structure appears. Under ambient conditions, the YN 10 structure has a high energy density (9.33 kJ g−1). By calculating the phonon dispersion curve, the structure has better dynamic stability at 250 GPa. Seven structures (Y 2 N, YN, YN 2 , YN 3 , YN 5 , YN 8 , YN 10) that appear on convex hull graphs in all YN systems are also calculated. Their dynamics, mechanics and related electronic properties are described in the appendix. We hope that our theoretical research can facilitate future experimental realization and help to advance the research on nitrogen chains. • We have made a systematic and comprehensive calculation of Y–N system at 0–250 GPa. • The zigzag N 6 6− anion, N 18 -ring and N 10 cage have been found in P -1-YN 3 , P -1-YN 8 and Imm 2-YN 10, respectively. • We find the YN 10 structure has high energy density and YN 2 structure is stable at ambient pressure. [ABSTRACT FROM AUTHOR]

The properties of ZnN 6 has been studied under high pressure using first-principles calculations. Three high-pressure phases, metallic Cm phase, semiconductor P 1, and polymeric nitrogen I 4 1 md phases, have been observed at 2.3 GPa, 28 GPa, and 98 GPa, respectively. Through theoretical calculations indicate that the I 4 1 md phase is thermodynamically stable at 0 GPa, while the Cm phase and P 1 phase are not stable until the pressure of 20 GPa. Under the action of pressure, nitrogen atoms in the I 4 1 md phase form a new network structure. There is a certain charge transfer between zinc atoms and nitrogen atoms, thus forming the interaction between anions and cations, which also determines the stability of the I 4 1 md phase. Moreover, the N atom is in the sp2 and sp3 hybridization. The energy density of the I 4 1 md phase is about 4.70 kJ/g, which determines that it can be regarded as a promising HEDMs candidate. [ABSTRACT FROM AUTHOR]

The high-pressure investigation of the PbS nanocrystal quantum dots (NQDs) with large Bohr radius has been conducted by in situ high-pressure X-ray diffraction, high-resolution transmission electron microscopy and alternating current impedance spectroscopy experiments up to 41.0 GPa. PbS NQDs present a similar pressure-induced structure phase transition path to bulk and nanocrystal PbS. The electronic conduction and the ionic conduction coexist in PbS NQDs, and the resistivity is generally larger than bulk and nanocrystal PbS. Above 9.1 GPa, the deviatoric stress drives the fusion of the nanoparticles, which leads to the reduction or the disappearance of grain boundary effect as well as a great influence on the dielectric performance. • The structure phase transitions of PbS NQDs have been investigated up to 41.0 GPa. • There is a mixed ionic and electronic conduction in PbS NQDs from 1.8 to 35.4 GPa. • HRTEM confirms the fusion of the nanoparticles drives by the pressure. [ABSTRACT FROM AUTHOR]

• Both zigzag nitrogen chain and connected N 6 ring have been found in HgN 3. • The two structures can be synthesized at a modest pressure. • Coulomb attraction and covalent interaction are found to stabilize the compounds. Exploring the bonding properties and polymerization mechanism of the polymer phases of nitrogen-rich compounds is one of the goals of high-pressure research. Considering first-principles calculations, a particle swarm optimization structure search method has been used to study the structural evolution behavior of nitrogen in HgN 3 up to 200 GPa. Three new phases with P- 1, P 2 1 / m , and P- 1 structures at pressures of 38 GPa, 125 GPa, and 148 GPa are identified for the first time. The theoretical calculations show that the two P -1 structures are dynamically stable at 50 GPa and 200 GPa. In these two phases, the nitrogen atoms form an infinite one-dimensional zigzag chain and connected N 6 ring, respectively. Two stable structures have semiconductor properties throughout the stable pressure range, primarily due to sp 2 hybridization of nitrogen atoms. Our studies provide a theoretical basis for the synthesis of polymeric nitrogen in high-pressure experiments and indicate the direction for future studies of mercury azide. [ABSTRACT FROM AUTHOR]