Phase transitions in alkaline earth metals under pressure

Olijnyk, H.; Holzapfel, W. B.

doi:10.1016/0375-9601(84)90757-6

Cited by 152 publications

(128 citation statements)

References 14 publications

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“…Nevertheless, the values for the equilibrium volume V 0 , bulk modulus B 0 and its derivative BЈ 0 , which from our calculation are 42.19 Å 3 , 17.46 GPa, and 3.14, respectively, are in close agreement with the corresponding experimental parameters of the equations of state (20). Calculated volume collapse ⌬V/V of 1% and 7% at the cF4 3 cI2 and cI2 3 cP1 phase transitions, respectively, are also in good agreement with the experiment (14).…”

Section: Resultssupporting

confidence: 75%

“…Ca shows an interesting and unique phase transition sequence from a closed, packed structure at ambient pressure to an open one at high pressures, namely, a face-centered cubic cF4 to a body-centered cubic cI2 transition at Ϸ19.5 GPa (13,14), and a cI2 to a simple cubic cP1 phase transition at 32 GPa (14). This remarkable transition sequence was found to occur because of the same s-band to d-band electron transfer, and that at high pressures the valence band acquires a complete d-like character (15).…”

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confidence: 99%

“…The Sc-II phase was found to be superconducting (11) and recent observations show that T C also increases monotonically with pressure (12). Following through the arguments given above, one can expect Ca to undergo a similar transition to a complex phase at very high pressures.Ca shows an interesting and unique phase transition sequence from a closed, packed structure at ambient pressure to an open one at high pressures, namely, a face-centered cubic cF4 to a body-centered cubic cI2 transition at Ϸ19.5 GPa (13,14), and a cI2 to a simple cubic cP1 phase transition at 32 GPa (14). This remarkable transition sequence was found to occur because of the same s-band to d-band electron transfer, and that at high pressures the valence band acquires a complete d-like character (15).…”

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confidence: 99%

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Prediction of incommensurate crystal structure in Ca at high pressure

Arapan

Mao

Ahuja

2008

Proc. Natl. Acad. Sci. U.S.A.

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Ca shows an interesting high-pressure phase transformation sequence, but, despite similar physical properties at high pressure and affinity in the electronic structure with its neighbors in the periodic table, no complex phase has been identified for Ca so far. We predict an incommensurate high-pressure phase of Ca from first principle calculations and describe a procedure of estimating incommensurate structure parameters by means of electronic structure calculations for periodic crystals. Thus, by using the ab initio technique for periodic structures, one can get not only reliable information about the electronic structure and structural parameters of an incommensurate phase, but also identify and predict such phases in new elements.ab initio calculations ͉ alkali metals T he continuous improvement of the high-pressure technique and the advances in the methods of characterization of materials under high pressure have opened new perspectives for materials physics community. The discovery of a series of phases for periodic table elements within the explored interval of pressures (1, 2) have stimulated an increased interest from both experimentalists and theoreticians to understand the unexpected behavior of simple elements under high pressure. Within the alkali and earth-alkaline metals, a series of complex structures at high pressure have been identified and, in particular, the complex phases of Ba-IV (3), Sr-V (4), Rb-IV (5), and K-III (6) have been determined as composite host-guest structures, which are incommensurate along the common axis of host and guest sub-lattices. The occurrence of such complex composite structures in a large number of elements and the robustness of these complex phases over a wide range of pressures and temperatures make the existence of composite incommensurate structures an intrinsic high-pressure phenomenon. Therefore, other elements may undergo similar high-pressure phase transitions. The nature of the transition to a composite structure is not completely understood yet, partly, because such an essential theoretical tool for describing the condensed matter as electronic structure calculations cannot be directly applied to study an incommensurate structure. However, one can perform first-principles calculations on commensurate analogues of an incommensurate phase and, indeed, such calculations can reproduce the phase transition sequence in close agreement with the experiment and provide reliable information about the electronic structure (7,8). Ab initio calculations of Ba-IV commensurate analogue (7) suggest that the transition from a closed, packed structure at low pressure to a more open, complex structure at high pressure might be because of the transfer of electrons from free-electron like s-bands to more directional d-bands. In the Ba-IV phase, the sd-hybridization occurs between the orbitals of two nonequivalent Ba atoms: guest atoms with a more d-like character and host atoms with a more s-like character. Therefore, from the electronic structure perspective, the composite s...

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Section: Resultssupporting

confidence: 75%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Prediction of incommensurate crystal structure in Ca at high pressure

Arapan

Mao

Ahuja

2008

Proc. Natl. Acad. Sci. U.S.A.

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“…The series of surprising high-pressure phase transitions (6)(7)(8)(9) that change the elemental Ca from an ordinary metal to the highest known T c (>25 K) elemental superconductor (8) has emerged as a central topic as demonstrated in many concurrent investigations (10-17) but also presented a seemingly irreconcilable gap between theory and experiment. X-ray diffraction (XRD) at 300 K indicates that Ca transforms from its ambient condition fcc structure Ca-I to bodycentered cubic (bcc) Ca-II at 20 GPa and then to simple-cubic (sc) Ca-III at 32 GPa (7,9,18). At higher pressures, Ca-III undergoes two additional transformations, to Ca-IV and V at 119 and 143 GPa, respectively (7,9,18).…”

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confidence: 99%

Distortions and stabilization of simple-cubic calcium at high pressure and low temperature

Mao

Wang

Ding

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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“…The critical role of the pressure-induced s to d band electron transfer on the structural stability and physical properties, such as superconductivity, of metals has been studied extensively over the years [1][2][3][4]. High pressure structural sequences in 3 rd period metals have also been elucidated when taking into account the lowering and filling under compression of the initially vacant d-band [5,6].…”

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confidence: 99%