The structural transition from NaCl to CsCl type in cesium hydride

Bashkin, I. O.; Degtyareva, V.F.; Dergachev, Yu. M.; Ponyatovskiĭ, E. G.

doi:10.1002/pssb.2221140252

Cited by 22 publications

(7 citation statements)

References 8 publications

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“…Bashkin et al [7] have also measured the pressure dependence of the volume of CsH. They found the same volume change at the transition, and their value of the bulk modulus in the NaCl-type structure (B0 = 8.1 GPa) is in good agreement with our value of 7.6 ± 0.8 GPa.…”

Section: Discussionsupporting

confidence: 90%

High Pressure X-Ray Investigation of the Alkali Hydrides NaH, KH, RbH, and CsH*

Hochheimer¹,

Strössner²,

Hönle³

et al. 1985

Zeitschrift Für Physikalische Chemie

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Section: Discussionsupporting

confidence: 90%

High Pressure X-Ray Investigation of the Alkali Hydrides NaH, KH, RbH, and CsH*

Hochheimer¹,

Strössner²,

Hönle³

et al. 1985

Zeitschrift Für Physikalische Chemie

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“…In fact, transition-metal hydrides are considered to be covalent materials, whereas alkali hydrides are structurally rather similar to the corresponding halides. Understanding the behavior of these materials at high pressure would presumably allow to better characterize the bonding properties of hydrogen in extreme pressure conditions and thus provide valuable hints towards the long searched goal of hydrogen metallization.Alkali hydrides at zero pressure crystallize in the rocksalt (cubic B1) structure, while most of them undergo a transition to the cubic B2 (CsCl-like) structure at an applied pressure of a few GPa [10,11,12]. Recently, a second transition from the B2 structure to a new orthorhombic phase has been observed to occur in CsH at an applied pressure of about 17 GPa [13].…”

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confidence: 99%

Phonon Softening and Elastic Instabilities in the Cubic-to-Orthorhombic Structural Transition of CsH

1997

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The cubic-to-orthorhombic structural transition occurring in CsH at a pressure of about 17 GPa is studied by ab initio calculations. The relative stability of the competing structures and the transition pressure are correctly predicted. We show that this pressure-induced first-order transition is intimately related to a displacive second-order transition which would occur upon application of a shear strain to the (110) planes. The resulting instability is rationalized in terms of the pressure-induced modifications of the electronic structure. [S0031-9007(97)03462-5] PACS numbers: 64.70. Kb, 62.50. + p, 63.20.Dj, 63.70. + h In recent years the availability of the diamond anvilcell technology [1] has renewed the interest in the highpressure properties of alkali halides which are the simplest and prototypical among ionic solids. In the case of cesium halides, these studies have been carried out especially in the search of band-overlap metallization which occurs at pressures in the Mbar range. In the quest of metallization, unexpected phase transformations to tetragonal and orthorhombic structures have been observed experimentally [2-6] and studied theoretically [6][7][8][9].Metal hydrides are considerably more covalent than the corresponding halides. In fact, transition-metal hydrides are considered to be covalent materials, whereas alkali hydrides are structurally rather similar to the corresponding halides. Alkali hydrides at zero pressure crystallize in the rocksalt (cubic B1) structure, while most of them undergo a transition to the cubic B2 (CsCl-like) structure at an applied pressure of a few GPa [10 -12]. Recently, a second transition from the B2 structure to a new orthorhombic phase has been observed to occur in CsH at an applied pressure of about 17 GPa [13]. The new phase has been assigned the CrB structure which belongs to the D 17 2h space group. In order to assess the driving mechanisms of this transition we have undertaken a series of first-principles calculations of the electronic, structural, elastic, and vibrational properties of CsH as well as of their dependence upon pressure. To this end, we have employed density-functional theory (DFT) within the local-density approximation (LDA) [14], and its gradient-corrected (GC) generalizations [15]. Our calculations have been performed using norm-conserving pseudopotentials [16]. In the case of Cs, 5s and 5p semicore states have been treated as valence states. For LDA calculations we have used the same Cs potential as in Ref.[8], while hydrogen is described by a norm-conserving pseudopotential constructed for the 1s wave function, so as to smoothen it somewhat and make our calculations well converged with the 25 Ry kinetic-energy cutoff which we use. New potentials have been generated for GC calculations. The vibrational properties are determined using the densityfunctional perturbation theory (DFPT) [17].In Table I we report our results for some structural properties of CsH in the three phases studied here: B1, B2, and CrB. The LDA fails to account for...

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“…At ambient pressure, the alkali hydrides have the NaC1 81 structure and, with the exception of LiH, have been observed to transform to the CsCl 82 structure at elevated pressures [2, 6,7]. Their counterparts, the alkali halides, crystallize into the NaC1 Bl structure or the CsC1 82 structure at room pressure.…”

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New High Pressure Crystal Structure and Equation of State of Cesium Hydride to 253 GPa

et al. 1995

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A new orthorhombic high pressure phase was observed in CsH at approximately 17.5 GPa and V/Vp = 0.53. This high pressure phase was assigned to the CrB structure with the Cmcm space group based upon 19 x-ray diffraction peaks. It was studied to V/Vo = 0.260 at 253 GPa. This is the highest compression measured in the ionic alkali hydrides to date. At 253 GPa, the bulk modulus of CsH (881 GPa) is nearly double that of diamond at atmospheric pressure (442 GPa). PACS numbers: 62.50.+p, 61.10.Lx, 64.30.+t, 64.60.i In metallic hydrides the hydrogen particle forms both covalent and ionic bonds. At ambient pressure, transition metal hydrides have covalent bonding, whereas alkali metal hydrides are principally ionic [1]. The alkali halides are assumed to have a complete charge transfer of 1.0e between alkali anions and halide cations. By comparison, the alkali hydrides are computed to have a charge transfer of 0.73e [2]. While more covalent than the alkali halides, the alkali hydrides are crystallographically similar to the alkali halides and are expected to behave similarly with the increasing pressure.

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The structural transition from NaCl to CsCl type in cesium hydride

Cited by 22 publications

References 8 publications

High Pressure X-Ray Investigation of the Alkali Hydrides NaH, KH, RbH, and CsH*

High Pressure X-Ray Investigation of the Alkali Hydrides NaH, KH, RbH, and CsH*

Phonon Softening and Elastic Instabilities in the Cubic-to-Orthorhombic Structural Transition of CsH

New High Pressure Crystal Structure and Equation of State of Cesium Hydride to 253 GPa

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