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We have investigated the size-dependent high pressure behavior of nanocrystalline TiN using an angle-dispersive X-ray diffraction technique in a diamond-anvil cell at room temperature. No phase transition was observed during compression for each sample. A fit of the pressure versus volume data to a second Birch–Murnaghan equation yielded the following parameters for 16nm, 34nm and 80nm, zero-pressure volume, V 0=75.77Å3, 75.98Å3 and 76.06Å3, bulk modulus, B 0=320(7)GPa, 338(6)GPa and 287(3)GPa, respectively. This result along with a reanalysis of previous studies on TiN indicates that the bulk modulus first increases and then decreases with decreasing grain size. The compressibility of TiN has a minimum at ~34nm. [ABSTRACT FROM AUTHOR]

Abstract: Phase transitions of both α-BiNbO4 and β-BiNbO4 were investigated under high pressure and high temperature (HPHT) (0–5GPa and 300–1800°C, respectively) using X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive spectroscope (EDS). The stable regimes for the BiNbO4 phases were also determined. Experiments showed that both α-BiNbO4 and β-BiNbO4 could convert to a new high pressure phase HP-BiNbO4 above 3GPa, and the transition temperatures decreased with increasing pressures. Below 3GPa, β-BiNbO4 keeps stable up to 1800°C, while α-BiNbO4 converts to β-BiNbO4 when temperature is higher than 1150°C. By heating the metastable HP-BiNbO4 phase at room pressure, HP-BiNbO4 converts to α-BiNbO4 at 600°C. Above 1150°C, HP-BiNbO4 would transform to β-BiNbO4. Phase relationships of Bi2O3, Nb2O5, α-BiNbO4, β-BiNbO4 and HP-BiNbO4 were also summarized. [Copyright &y& Elsevier]

Abstract: In general, the high-density state is a preferred state of materials under high pressures. In this study, however, when the LiBO2–Al2O3 system quenched from melts at the cooling rate of 50–60 °C/s under high pressures, low density - Al2O3 was synthesized from high density - Al2O3, with a 7.1% volume expansion of Al2O3. While those samples which are quenched at the same cooling rate under a lower pressure appeared to be glassy. The minimal pressure synthesized the low-density - Al2O3 or the maximal glass forming pressure was decreased with increasing content of Al2O3 below its saturation point in LiBO2 melt. [ABSTRACT FROM AUTHOR]

The new melting curve of cobalt (Co) was determined to be 12 GPa using the in situ high-pressure temperature measurement method (HPTM) in a high-volume cubic press using two melting criteria: first, plateaus in the temperature vs power functions in situ experiments, and second, the texture changes in the samples before and after high-pressure high-temperature (HP-HT) treatments with a scanning electron microscope (SEM). The slope of the melting point with increasing pressure was approximately 33 K/GPa in our experimental pressure range and progressively decreased under further compression. Our new melting curve of Co under high pressure is reasonably consistent with the simulation results using one-phase and two-phase calculations and has a similar trend with the reported melting curves of Fe and Ni. • We show the in situ high-pressure temperature measurement method in the large volume cubic press that was an effective and simple method to measure the melting point. • Two melting criteria were used: firstly, plateaux in temperature vs. power functions in in situ experiments and secondly, the texture changes for the samples before and after high-pressure high-temperature treatments with a scanning electron microscope. • The slope of melting point with increasing pressure was found to be about 33 K/GPa in our experimental pressure range and progressively decreases under a further compression. • Our new melting curve of Co under high pressure is reasonably consistent with the simulation results using one-phase and two-phase calculations and has a similar trend with the reported melting curves of Fe and Ni. [ABSTRACT FROM AUTHOR]

In the present work, the orthorhombic (α) BiNbO 4 have been investigated with the in-situ angle-dispersive x-ray diffraction (ADXRD) measurements under high pressure. Pressure-induced phase transition was observed in α-BiNbO 4 , and compressibility of the unit cell axes (a, b and c axes) of α-BiNbO 4 shows an anisotropic with pressure increasing. The phase transition routine and the effect of pressure in the phase evolution of BiNbO 4 were also explored. The results indicate that pressure-induced phase transition is reversible, in contrast, pressure and temperature-induced phase transition is irreversible in system of BiNbO 4 , but the phase remains stable without pressure. High pressure plays a critical role and provides a driving force for phase transition of BiNbO 4 . [ABSTRACT FROM AUTHOR]

The phase transition of PbNiO3 from LiNbO3 structure to the perovskite structure has been observed between 4.4 and 9.5 GPa, which was investigated by high-pressure synchrotron x-ray powder diffraction at room temperature. Compression behavior of the two phases has been analyzed, and the c axis is the soft direction for LiNbO 3-type PbNiO3. The bulk modulus of the LiNbO3-type PbNiO3 is K0=184(3) GPa, K0′=4.5(9), and the perovskite type is K0=166(8) GPa, K0′=4.9(8). [ABSTRACT FROM AUTHOR]

A widely investigated allotrope of germanium, metastable germanium (ST12 Ge), has garnered sustained interest for quite a few years since it has been applied as a potential semiconductor component owing to its optical properties. In this study, a large pure bulk sample of ST12 Ge was synthesized through secondary pressure induced phase transition. The structure and purity of the sample were characterized via a combination of powder X-ray diffraction, Raman scattering, and X-ray photoelectron spectroscopy. Moreover, its thermal stability and optical properties were investigated. The bandgap structure, Vickers hardness, Raman spectrum, and other properties under pressure, were systematically investigated via first principles calculations. • First, in this study, phase-pure ST12 Ge bulks were prepared through secondary pressure induced phase transition. • Second, the structure and purity of the sample have been studied. The thermal stability and optical properties were investigated in details. • Third, first-principle calculations were used to calculate the its bandgap structure, Vickers hardness, Raman spectrum and other properties under pressure. [ABSTRACT FROM AUTHOR]

Abstract: This work presents a comprehensive study on phase transition in NaGaO2 under high pressure and temperature (P–T) conditions. X-ray diffraction (XRD) was used to identify the phase composition of the recovered samples. Our results revealed that NaGaO2 could undergo a structural phase transition from orthorhombic - NaGaO2 to hexagonal - NaGaO2 under high pressure and temperature. The pressure–temperature phase boundaries of NaGaO2 were determined up to 5 GPa and 2073 K. The hexagonal - NaGaO2 sample recovered from higher pressure and temperature exhibited a highly (003) preferred orientation. Besides, a reversible transition from - to - NaGaO2 was observed above 473 K under normal-pressure condition. The high-pressure melting curve of NaGaO2, for the first time, was measured by using in-situ thermal measurement. [Copyright &y& Elsevier]

Abstract: We report on the in situ electrical resistance measurements of Ti2AlC under high pressure up to 6 GPa using four-probe method in a cubic large volume press. The resistance of Ti2AlC changes smoothly with pressure without sharp anomalies, which reveals no phase transformations. The resistivity decreases with increasing pressure. At pressures above 3.5 GPa, the resistivity decreases slowly with a pressure dependence of about . In addition, the resistivity was also measured at the process of decompression. The resistivity changes slowly with a pressure dependence of about at pressures above 2.5 GPa. These results are associated with the resistivity change with temperature and could confirm that the transition metal plays the dominant role in electrical transport. [Copyright &y& Elsevier]