title: The synthesis of unconventional stoichiometric compounds in the K-Br system at high pressures.
abstract: 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 KBr3and KBr5, 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 Br2resulted in the formation of orthorhombic KBr3at ∼2.0 GPa. Further compression led to the formation of monoclinic KBr5at ∼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, KBr5remained stable down to 5.0 GPa. High-pressure (14-20 GPa) and high-temperature (>1500 K) laser heating experiments showed the decomposition of KBr5into KBr3(trigonal) and Br2with 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.
authors.affiliation: High Pressure & Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Trombay-400 085, India. msunder@barc.gov.in.
authors.forename: Nishant N
authors.initials: NN
authors.lastname: Patel
authors.affiliation: High Pressure & Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Trombay-400 085, India. msunder@barc.gov.in.
authors.forename: Ashok K
authors.initials: AK
authors.lastname: Verma
authors.affiliation: High Pressure & Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Trombay-400 085, India. msunder@barc.gov.in.
authors.forename: A K
authors.initials: AK
authors.lastname: Mishra
authors.affiliation: High Pressure & Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Trombay-400 085, India. msunder@barc.gov.in.
authors.forename: Meenakshi
authors.identifier: http://orcid.org/0000-0002-4026-1665
authors.initials: M
authors.lastname: Sunder
authors.affiliation: High Pressure & Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Trombay-400 085, India. msunder@barc.gov.in.
authors.forename: Surinder M
authors.initials: SM
authors.lastname: Sharma