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Recently, the search for and synthesis of unconventional stoichiometric compounds have become one of the most active areas of high pressure research. Here, we report the synthesis of two new stoichiometric compounds, namely KBr and KBr, at high pressures in the K-Br system. Until now, KBr was the only known compound in this system. Two independent experimental techniques, namely Raman spectroscopy and X-ray diffraction measurements, were employed to detect and confirm the formation of the new compounds. A room temperature chemical reaction between KBr and Br resulted in the formation of orthorhombic KBr at ∼2.0 GPa. Further compression led to the formation of monoclinic KBr at ∼6.0 GPa. This was accompanied by an anomalously large pressure (>2 GPa) increase inside the sample chamber and it remained stable up to the highest pressure, 24 GPa, of our study. Upon decompression, KBr remained stable down to 5.0 GPa. High-pressure (14-20 GPa) and high-temperature (>1500 K) laser heating experiments showed the decomposition of KBr into KBr (trigonal) and Br with a large volume reduction. First-principles structural searches were carried out to solve the composition and related crystal structures. The proposed structures give good description of the experimental Raman spectra and X-ray diffraction data. The electronic structure calculations reveal semiconducting behaviour for these compounds.

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The melting curve of osmium (Os) has been determined up to 35 GPa and 5800 K using a laser heated diamond anvil cell facility. Al2O3 was used as the thermal insulator and pressure transmitting medium. Melting was detected by the laser speckle method, and spectroradiometric technique was employed for determination of melting temperature. The measured melting curve has been compared with available theoretical melting curves. The Simon-Glatzel fit to the experimental data agrees reasonably well with the recently reported theoretical melting curve using Z-method. The melting slope of the measured melting curve is 58.0 K/GPa at P = 0.1 MPa. The melting line of Os is seen to cross that of W around 6 GPa, making it the most refractory metal. The density dependence of Grüneisen parameter [γ(ρ)] has also been determined analytically, using the experimentally obtained melting slope.

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