Room-temperature ferromagnetism has been observed in Y-doped AlN (AlN:Y) nanorods. Our first-principle calculations have demonstrated that the ferromagnetism in AlN:Y is from Al vacancies and that the introduction of nonmagnetic rare-earth element Y into AlN can significantly reduce the formation energy of Al vacancy which leads to high Al vacancies responsible for the observed ferromagnetism in AlN:Y nanorods. These findings illustrate an efficient way to reduce the formation energy of cation vacancy by doping nonmagnetic elements, such as Y, leading to ferromagnetism in semiconductors.

•The fcc′→C2/m →α-U→bct transition of Cerium is clearly observed at high pressure.•The growth of grains in α-U structure is driven by the phase interface mismatch of α-U and fcc′.•Prepressed condition is a feasible method for the phase transition research at high pressure.•The high pressure crystal structures of Cerium are confirmed by full Rietveld refinement.A fascinating structure transition of cerium around 5 GPa has been studied using high-resolution synchrotron angle-dispersive powder diffraction techniques. This study indicates that the structural transition of cerium strongly depends on the process of compression. Two runs experiments with different compression conditions demonstrate two different structural transition sequences at room temperature around 5 GPa, fcc′→C2/m →bct for regular compression, fcc′→C2/m →α-U→bct for the pre-compression. These results show that pressure is not the only factor to determining structural transformation at high pressure, and the structural transformation sequences can be varied by changing the external conditions e.g. pre-compression.

GaN:Mn nanoparticles were synthesized successfully by DC arc discharge plasma without any catalyst or template. X-ray diffraction patterns revealed that all peaks position of GaN:Mn nanoparticles were shifted towards larger angles, indicating the c lattice parameter of GaN:Mn is smaller than that of GaN due to the lattice distortion. The growth mechanism explains the characteristic of morphology and size. The room temperature photoluminescence (PL) of GaN:Mn nanostructure exhibits a relatively broad range of visible light absorption due to dopant-induced energy levels within the band gap increasing the yield for electron–hole pair formation under illumination with visible light. The magnetic properties were investigated by VSM and quantum design MPMS SQUID. Mn doped GaN nanoparticles show two prominent critical points corresponding to the magnetic phase transition, respectively. One is the classical thermally driven from superparamagnetic (SP) to blocked SP, the other is the quantum tunneling of magnetization from magnetic long-range order to quantum superparamagnetic (QSP) state. The magnetism is derived from the Mn atoms, the magnetic coupling between Mn atoms depends on the mediating of N.

Synchrotron X-ray diffraction (XRD) is performed on BaF2 nanoparticles to study the structural phase transition up to about 30 GPa under ambient temperature. We observed that the cubic structure in BaF2 nanoparticles is stable up to 6.8 GPa, a level much higher than that in bulk BaF2. Pressure-induced amorphization (PIA) occurs in BaF2 nanoparticles under compression, which results in a high-density amorphous (HDA) form. Upon pressure release, a low-density amorphous (LDA) form is maintained at ambient conditions. This study is the first to demonstrate that PIA and polyamorphism exist in BaF2 nanomaterials and that finite grain size plays a critical role in inducing PIA and polyamorphism.

Two-dimensional tin selenide (SnSe) nanosheets were synthesized using a plasma-assisted direct current arc discharge method. The structural characterization indicates that the nanosheets are single-crystalline with an average thickness of ∼25 nm and a lateral dimension of ∼500 nm. The high pressure behaviors of the as-synthesized SnSe nanosheets were investigated by in situ high-pressure synchrotron angle-dispersive X-ray diffraction and Raman scattering up to ∼30 GPa in diamond anvil cells at room temperature. A second-order isostructural continuous phase transition (Pnma → Cmcm) was observed at ∼7 GPa, which is considerably lower than the transition pressure of bulk SnSe. The reduction of transition pressure is induced by the volumetric expansion with softening of the Poisson ratio and shear modulus. Moreover, the measured zero-pressure bulk modulus of the SnSe nanosheets coincides with bulk SnSe. This abnormal phenomenon is attributed to the unique intrinsic geometry in the nanosheets. The high-pressure bulk modulus is considerably higher than the theoretical value. The pressure-induced morphology change should be responsible for the improved bulk modulus.

Room-temperature ferromagnetism has been observed in Mg-doped AlN (AlN:Mg) nanowires. The saturation magnetization and the coercivity of the AlN:Mg nanowires are about 0.051 emu g−1 and 127 Oe, respectively. The Al vacancy and substitutional Mg could play very important roles in room temperature ferromagnetism. These findings confirmed the room temperature ferromagnetism in diluted magnetic semiconductor AlN:Mg nanowires by doping with the nonmagnetic element Mg.

High-pressure Raman scattering studies are performed on acetonitrile in a diamond anvil cell up to 24.8 GPa at room temperature. The results show that liquid acetonitrile transforms into β phase at 0.3 GPa, and then into α phase at 0.8 GPa. With increasing pressure, the α to γ phase transition is observed at 9.8 GPa which results from the rearrangement of molecular structure. After further increasing the pressure to 21.5 GPa, the external Raman modes of acetonitrile completely disappear, and the result suggests that acetonitrile ultimately turns into an amorphous state accompanying the decreases of transmittance light. The high pressure behaviors of polar molecular acetonitrile will provide important information for the study of lattice dynamics of molecular crystals.

In situ X-ray diffraction studies of rare-earth metals Sc- and Y-doped AlN nanoprisms were carried out using angle-dispersive synchrotron radiation technique in a diamond anvil cell up to approximately 40 and 35 GPa, respectively. Pressure-induced wurtzite-to-rocksalt phase transitions start at 18.6 and 16.2 GPa and complete at 29.8 and 26.5 GPa, showing lower phase-transition pressures compared with bulk AlN and AlN nanowires while slightly higher than that of AlN nanocrystals. The effects of volume expansion, volume collapse, and crystal defects on phase transition have been discussed. The distinct high-pressure behaviors can be explained in terms of the doping-induced Al vacancy defects along with substitute ions sit at the cation sites, which lead to the distortion of the crystal structure that reduce the structural stability of the doped AlN nanoprisms.

Using an in situ synchrotron angle-dispersive X-ray diffraction technique, two morphologies of nanocrystalline SrF2 (i.e., nanoparticles and nanoplates) with different sizes of 11 and 21 nm were compressed up to ∼46 GPa in diamond anvil cells at room temperature. We observed that two phase transitions of the SrF2 nanoparticles occur at 10.0 and 34.3 GPa, which are much higher than those in bulk SrF2. Upon decompression, the pure α-PbCl2-type metastable phase is retained when the pressure is released. In contrast, high-pressure behavior of the SrF2 nanoplates is similar to that of bulk material. Such distinct high-pressure behaviors in two synthesized SrF2 nanocrystals have been discussed in terms of volume expansion, exposed crystal plane, morphology, and defects. Further analysis shows that the defect effect is believed to be the major factor to affect the high-pressure behaviors in two synthesized nanocrystalline SrF2.

High-pressure Raman scattering and synchrotron angle-dispersive X-ray diffraction studies have been performed on liquid ammonia hemihydrates (2NH3·H2O) at room temperature up to 41.0 GPa. The results demonstrate that liquid 2NH3·H2O transforms into a solid phase at 3.5 GPa. Upon increasing pressure, a solid-solid phase transition is observed at about 19.0 GPa. When pressure is increased up to 25.8 GPa, another solid-solid phase transition is obtained. The first solid-solid phase transition at about 19.0 GPa originates from the rotation of type II ammonia molecule via the O–H⋯N bond, and this phase transition is from orthorhombic to body-centered-cubic. High-pressure Raman scattering and X-ray diffraction results of 2NH3·H2O provide significant information for better understanding the physical properties of the ammonia–water binary system under extreme conditions, and further for the structure state of the outer planets and large satellites in the solar system.

The high-pressure behavior of SrF2 has been investigated by angle-dispersive synchrotron X-ray powder diffraction measurement up to 50.3 GPa at room temperature. Two phase transformations were observed at 6.8 and 29.5 GPa, and the two high pressure phases were identified as orthorhombic (Pnma) phase and hexagonal (P63/mmc) phase by Rietveld refinement. Upon decompression, retransformation was observed and the sample recovered under ambient conditions consisted of a mixture of cubic phase and orthorhombic phase. The compressing characteristics of SrF2 as the pressure increases were discussed, indicating higher incompressibility of SrF2 under high pressure.Graphical abstractThe high-pressure behavior of SrF2 has been investigated by angle-dispersive synchrotron X-ray powder diffraction measurement up to 50.3 GPa at room temperature.Highlights► The high-pressure study on SrF2 up to 50.3 GPa at room temperature. ► Two first-order phase transformations were observed at 6.8 and 29.5 GPa. ► The three stable structures are confirmed by Rietveld refinements. ► The cubic and orthorhombic phase co-exist at pressures down to ambient pressure. ► The bulk modulus indicates higher incompressibility of SrF2 under high pressure.

We report here one-step synthesis of Si3N4 nanodendrites by selectively applying a vapor–solid (VS) and vapor–liquid–solid (VLS) strategy via direct current arc discharge method. The resultant nanodendrites were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy and X-ray powder diffraction. The spine-shaped nanodendrites were generated by a noncatalytic growth following a VS mode. The uniform secondary nanowire branches were epitaxial grown from two side surfaces of the nanowire stems. The pine-shaped nanodendrites were obtained through a catalytic growth in a VLS process. These branch nanowires were unsystematically grown from the nanocone-like stems. The photoluminescence spectra of the nanodendrites show a strong white light emission around 400–750 nm, suggesting their potential applications in light and electron emission devices.Graphical abstractSpine-shaped and pine-shaped Si3N4 hierarchical nanostructures were synthesized by VS and VLS mode with plasma-assisted dc arc discharge method. Highlights► Si3N4 stem–branch featured nanostructures have been prepared. ► Spine-shaped nanodendrites were generated by a noncatalytic growth following a VS mode. ► Pine-shaped nanodendrites were obtained through a catalytic growth in a VLS process.

Zn1−XMnXS (X=0.85%X=0.85% and 1.26%) nanoparticles have been synthesized using a specially designed equipment and we have studied the influence of doping Mn2+ on the surface energy of ZnS. The high pressure behaviors of ZnS nanocrystals with different dopant contents have been investigated using angle-dispersive synchrotron X-ray powder diffraction up to 45.1 GPa. Theoretical calculations show that doping with Mn2+ increases the surface energy of the nanocrystals. The theoretical result has been further corroborated by our experimental observation of an increase in the phase transition pressure of Mn2+ doped ZnS nanocrystals in diamond-anvil-cell studies.Research highlights► ZnS:Mn magnetic semiconductor nanocrystals are synthesized using an inorganic method. ► The phase transition pressure is higher in Mn2+ doped ZnS nanocrystals. ► Mn2+ doping of ZnS nanocrystals increases the surface energy of the nanocrystals. ► New experimental methods for achieving an understanding of the surface energies of nanomaterials are developed.

We performed high-pressure Raman scattering and angle-dispersive synchrotron X-ray diffraction measurements on n-heptane at room temperature. It has been found that n-heptane undergoes a liquid to rotator phase III (RIII) transition at 1.2 GPa and then transforms into another rotator phase RIV at about 3 GPa. As the pressure reaches 7.5 GPa, a transition from an orientationally disordered RIV phase to an ordered crystalline state starts and is completed around 14.5 GPa. Our results clearly present the high-pressure phase transition sequence (liquid–RIII–RIV–crystal) of n-heptane, similar to that of normal alkanes.

Aluminium nitride (AlN) branched nanostructures with tree shapes and sea urchin shapes are synthesized via a one-step improved DC arc discharge plasma method without any catalyst and template. The branched nanostructures with tree shapes and sea urchin shapes can be easily controlled by the location of collection. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies show that the branches of tree shaped nanostructures grow in a sequence of nanowires, nanomultipeds and nanocombs. The growth mechanisms of these branched nanostructures are discussed in detail. The optical properties of AlN branched nanostructures with tree shapes and sea urchin shapes are investigated.

The high-pressure Raman spectra of AlN nanowires have been measured up to 33.1 GPa. The phase transition from the wurtzite to rocksalt was found at about 24.4 GPa by the appearance of a new Raman signal. Above 24.4 GPa, a new Raman signal due to disorder-activated Raman scattering in the rocksalt phase was observed. The pressure coefficients, phase transition criterion, and transition path of AlN nanowires, which could be different from that of bulk AlN, are carefully discussed. The Raman signal of AlN nanowires recovered at ambient pressure from 33.1 GPa is similar to that of rocksalt-type AlN nanowires obtained previously after a high-pressure treatment to 51.1 GPa.

Novel AlN nanostructures with tunable building units of the architectures have been successfully synthesized without any catalyst or template; the subsequent photoluminescence (PL) indicates that the optical properties of the AlN nanostructures can be adjusted by tuning the architectures.

The high-pressure behavior of scandium oxide (Sc2O3) has been investigated by angle-dispersive synchrotron powder X-ray diffraction and Raman spectroscopy techniques in a diamond anvil cell up to 46.2 and 42 GPa, respectively. An irreversible structural transformation of Sc2O3 from the cubic phase to a monoclinic high-pressure phase was observed at 36 GPa. Subsequent ab initio calculations for Sc2O3 predicted the phase transition from the cubic to monoclinic phase but at a much lower pressure. The same calculations predicted a second phase transition at 77 GPa from the monoclinic to hexagonal phase.

The structural behavior of Mg3N2 has been investigated up to 40.7 GPa at room temperature by means of angle-dispersive X-ray diffraction. A reversible, first-order structural phase transition from the ambient cubic phase (Ia3̅) to a high-pressure monoclinic phase (C2/m) is found to start at ∼20.6 GPa and complete at ∼32.5 GPa for the first time. The equation of state determined from our experiments yields bulk moduli of 110.7(2) and 171.5(1) GPa for the cubic and monoclinic phases, respectively, indicating higher incompressibility of the high-pressure phase of Mg3N2. First-principles calculations reproduced the phase stability and transition pressure determined in our experiment. In addition, a second phase transition from the monoclinic phase to a hexagonal phase (P3̅m1) was predicted around 67 GPa for Mg3N2. The electronic band structures of three phases of Mg3N2 are also calculated and discussed.

Aluminum nitride (AlN) nanostructures have shown novel physical and chemical properties that are essential for technological applications. We report a vapor−solid growth of novel three-dimensional (3D) AlN urchin-like nanostructure in DC arc plasma via the direct reaction between Al vapor and N2 gas without any catalyst or template. The as-prepared 3D AlN nanostructures which have urchin-like shapes consist of numerous microdaggers with sharp tips and lengths of up to several micrometers and widths of 0.5−2 μm. A growth mechanism of AlN nanostructures with urchin shapes was suggested and explained in detail. The optical properties of the AlN nanostructures with urchin shapes were also studied with photoluminescence spectrum, which reveals a broad emission, suggesting potential applications in electronic and optoelectronic nanodevices.

The structural behavior of magnesium silicide (Mg2Si) was investigated in a diamond anvil cell (DAC) by energy dispersive synchrotron X-ray diffraction up to 41.3 GPa at room temperature. Two pressure-induced structural phase transitions for Mg2Si have been identified, at around 7.5 GPa and 21.3 GPa, respectively. The new structures of Mg2Si are in turn determined as orthorhombic phase with anti-cotunnite (Pnma,Z=4)(Pnma,Z=4) structure and hexagonal phase with Ni2In-type (P63/mmc,Z=2)(P63/mmc,Z=2) structure. Both the structural phase transitions are of first-order nature and are reversible.

The high-pressure behaviors of MOO3·1/2H2O and MOO3·2H2O have been investigated by Raman spectroscopy in a diamond anvil cell up to 31.3 and 30.3 GPa, respectively. In the pressure range up to around 30 GPa, both MOO3·1/2H2O and MOO3·2H2O undergo two reversible structural phase transitions. We observed a subtle structural transition due to O−H···O hydrogen bond in MOO3·1/2H2O at 3.3 GPa. We found a soft mode phase transition in MOO3·2H2O at 6.6 GPa. At higher pressures, a frequency discontinuity shift and appearance of new peaks occurred in both MOO3·1/2H2O and MOO3·2H2O, indicating that the second phase transition is a first-order transition. The frequency redshift of the O−H stretching bands of MOO3·1/2H2O and MOO3·2H2O are believed to be related to the enhancement of the O−H···O weak hydrogen bonds under high pressures.

Hexagonal and truncated hexagonal shaped MoO3 nanoplates (MoO3 HNP) were synthesized through a simple vapor-deposition method in Ar atmosphere under ambient pressure without the assistant of any catalysts. The structure and morphology of MoO3 HNP were investigated by XRD, EDX, SEM, TEM, and HRTEM. The results reveal that the HNP are α-MoO3 and have a large area surface. The Raman spectrum shows a significant size effect on the vibrational property of MoO3 HNP. The photoluminescence (PL) spectrum was carried out, and two peaks at 351 and 410 nm were observed in the spectrum. In addition, a possible growth mechanism proposed as VS is discussed in detail.

High-pressure methods were applied to investigate the structural stability and hydrogen bonding of polar molecules of iodoform by synchrotron radiation X-ray diffraction and Raman spectra measurements, respectively. Up to a pressure of 40 GPa, no phase transitions were observed. The discontinuous frequency shift of the C−H stretching band is believed to be related to the enhancement of the C−H···I weak hydrogen bonds under high pressures. Ab initio calculations were performed, and the results predict the frequency shift of the C−H stretching vibration as C−H···I interacts via hydrogen bonding. The bulk modulus is 17.3 ± 0.8 GPa, with a pressure derivative of 5.2.

Novel three-dimensional AlN microroses, for the first time, have been synthesized via direct reaction between Al and N2 in arc plasma without any catalyst and template.

Nanocrystalline chromium nitride (CrN) with the cubic rock-salt structure was synthesized by the arc discharge method in nitrogen gas (N2). The product was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that the nitrogen gas pressure is a crucial factor for the synthesis of cubic CrN. At relatively low N2 pressure, cubic CrN was formed. With the increase of N2 pressure, hexagonal Cr2N and metal Cr were gradually formed. It indicated that the formation of CrN apparently favors a low nitrogen pressure environment, and the diffusion of nitrogen atoms into the Cr was lowered with the increase of N2 pressure. We explain this experimental observation in terms of the evaporation rate of anode Cr and the ionization of nitrogen.

An array of pine-shaped nanostructures of aluminum nitride (AlN) was synthesized through direct reaction between Al vapor and nitrogen gas in direct current (DC) arc discharge plasma without any catalyst or template. The as-prepared nanostructure consists of many pine-needle-shaped leaves with conical shape tips. The structure, morphology, and optical property of the nanostructure have been characterized by X-ray powder diffraction, energy-dispersive X-ray spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, and photoluminescence. A possible growth mechanism of the pine-shaped nanostructure was discussed. Two factors were found to be essential for branched nanostructure growth, i.e., the reaction time and N2 pressure. The photoluminescence spectrum of the nanostructure of AlN revealed an intense emission band, suggesting that there may be potential applications in electronic and optoelectronic nanodevices.

Zn1−XMnXS (X=0.85% and 1.26%) nanoparticles have been synthesized using a specially designed equipment and we have studied the influence of doping Mn2+ on the surface energy of ZnS. The high pressure behaviors of ZnS nanocrystals with different dopant contents have been investigated using angle-dispersive synchrotron X-ray powder diffraction up to 45.1 GPa. Theoretical calculations show that doping with Mn2+ increases the surface energy of the nanocrystals. The theoretical result has been further corroborated by our experimental observation of an increase in the phase transition pressure of Mn2+ doped ZnS nanocrystals in diamond-anvil-cell studies.Research highlights► ZnS:Mn magnetic semiconductor nanocrystals are synthesized using an inorganic method. ► The phase transition pressure is higher in Mn2+ doped ZnS nanocrystals. ► Mn2+ doping of ZnS nanocrystals increases the surface energy of the nanocrystals. ► New experimental methods for achieving an understanding of the surface energies of nanomaterials are developed.

Novel three-dimensional AlN microroses, for the first time, have been synthesized via direct reaction between Al and N2 in arc plasma without any catalyst and template.

Novel AlN nanostructures with tunable building units of the architectures have been successfully synthesized without any catalyst or template; the subsequent photoluminescence (PL) indicates that the optical properties of the AlN nanostructures can be adjusted by tuning the architectures.