Influence of high hydrostatic pressure on the crystal structure of BaFCl in the pressure range up to 6.5 GPa

Abstract

High-pressure X-ray diffraction measurements were made with BaFC1 single crystals (space group P4/nmm) using a diamond-anvil cell on a four-circle diffractometer (six data sets, 30 to 50 reflections, R values ranging from 2.5 to 5.0%). This compound does not show a pressure-induced phase transition up to 6.5 GPa at ambient temperatures. At lower pressures the compressibility of the c axis is larger than that of the a axis. At 2 GPa the compressibility becomes isotropic and at higher pressures again anisotropic, but now with an increasing c/a ratio. Such effects of pressure and the changes in positional parameters are discussed in comparison with the known structural data for a whole series of PbFCl-type compounds. Changes in the ion 'size' are accompanied by distortions of the structural framework leading to a more efficient packing. While the Madelung number decreases during this process, the relative loss of ionic lattice energy is compensated for by an increase in interactions due to polarization, which can be traced by the movement of the Ba 2+ ions within their coordination sphere. IntroduetlonIt is remarkable that mixed-anion compounds MFX with larger cations M mostly crystallize with the same structural arrangement regardless of the large differences in size and polarizability of the atoms found in such compounds. It has been stated that this variety in constituents leads to different 'branches' of the structure type, of which one -the PbFC1 type ( Fig. 1) -contains compounds with mainly ionic interactions, whereas another -coined as anti-Fe2As type -is encountered with compounds showing strongly covalent character, e.g. UPS (Flahaut, 1974;Johnson & Jeitschko, 1973). ' 0108-7681/83/040401-04501.50 We have emphasized that, within its field of existence, the PbFC1 type itself shows marked variations with respect to crystal geometry and even bonding. The structural differences within this arrangement, ranging from a coordination lattice (found with MOC1, MFCI and MHC1 compounds) to a layer structure (MOI, MFI, MHI), have been discussed by B~irnighausen, Brauer & Schultz (1965).A detailed analysis of well refined structures of fluorohalides (Beck, 1979) has shown an interesting correlation between positional parameters and the polarizability of the constituent ions. In the course of these studies it was our aim to trace the changes in bonding type induced by higher pressures by the same minute analysis of structural details.High-pressure X-ray investigations using powder specimens of fluorochlorides and -bromides of Eu, Sin, Pb and alkaline earths have shown no structural rearrangement up to pressures between 5 and 10 GPa (1 GPa = 10 kbar) (Beck, 1978a). The lattice constants of these compounds decrease linearly with pressure except for BaFC1, which was therefore chosen for further studies under high pressure using single crystals. © 1983 International Union of Crystallography INFLUENCE OF HYDROSTATIC PRESSURE ON THE STRUCTURE OF BaFC1Experimental BaFC1 crystals were prepared by sintering of the bin...

Pressure-Induced Martensitic Phase Transition and Low Lattice Thermal Conductivity of SrClF

“…Moreover, high-pressure research on PbClF-type materials has received tremendous interest owing to their quasi-2D layered structure, , which can provide an avenue for exploring pressure-induced layered to nonlayered structural phase transformations. Several high-pressure X-ray diffraction (HP-XRD) − and theoretical − studies were focused on understanding the high-pressure behavior of layered PbClF-type compounds. A HP-XRD study on MClF (M = Ca, Sr, Ba) and BaFBr compounds using a diamond anvil cell and synchrotron radiation revealed that CaClF and SrClF are stable up to 27 and 42 GPa, respectively.…”

Unraveling the Hidden Martensitic Phase Transition in BaClF and PbClF under High Pressure Using an Ab Initio Evolutionary Approach

“…Therefore, extensive studies have been devoted to understand the high pressure behavior of PbClF-type materials. High pressure X-ray diffraction measurements on BaClF single crystals reveal that BaClF is stable up to 6.5 GPa, it has isotropic compressibility at 2 GPa, and later it becomes anisotropic . Subramanian et al determined the structural stability of BaClF up to 35 GPa, and they observed a monoclinic ( P 2 1 / m ) phase at around 22 GPa.…”

“…High pressure X-ray diffraction measurements on BaClF single crystals reveal that BaClF is stable up to 6.5 GPa, it has isotropic compressibility at 2 GPa, and later it becomes anisotropic. 9 Subramanian et al 10 determined the structural stability of BaClF up to 35 GPa, and they observed a monoclinic (P2 1 /m) phase at around 22 GPa. Later, high pressure X-ray diffraction measurements 11,12 on MClF (M = Ca, Sr, Ba) and BaBrF compounds reveal that BaClF and BaBrF undergo structural phase transitions at 21 and 27 GPa, respectively.…”

Electronic structure, optical properties, and bonding in alkaline-earth halofluoride scintillators: BaClF, BaBrF, and BaIF

“…11,12 Finally, there have been a number of studies of the structural, vibrational, and high-pressure properties of these materials. [13][14][15][16][17][18][19][20][21][22][23][24][25][26] They show anisotropic compressibilities and interesting composition dependent phase transitions, including a transition to a monoclinic (P 2 1 /m) phase in BaClF at 22 GPa. Returning to the response to ionizing radiation, the behavior of these halofluorides is in sharp contrast to apparently closely related materials, such as BaF 2 and BaIBr.…”