Determination of the Structural Parameters of an Incommensurate Phase from First Principles: The Case of Sc-II

Arapan, Sergiu; Skorodumova, Natalia V.; Ahuja, Rajeev

doi:10.1103/physrevlett.102.085701

Cited by 17 publications

(17 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Thus, at high pressures we have a set of commensurate analogues, which approximate the incommensurate I4/mcm(00␥) structure with enthalpies lower than the enthalpy of the Ca-V structure. By fitting the calculated values of total energy of different commensurate analogues at a given volume with a smooth polynomial function, we can estimate the incommensurate ratio ␥, which gives the minimum of the energy curve E ϭ E(c 1 /c 2 ) at this volume (21).…”

Section: Resultsmentioning

confidence: 99%

Prediction of incommensurate crystal structure in Ca at high pressure

Arapan

Mao

Ahuja

2008

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

Self Cite

View full text Add to dashboard Cite

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...

show abstract

Section: Resultsmentioning

confidence: 99%

Prediction of incommensurate crystal structure in Ca at high pressure

Arapan

Mao

Ahuja

2008

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

Self Cite

View full text Add to dashboard Cite

show abstract

“…This also provides a first example of IC structure observed in non main-group elements [35]. The intriguing structural complexity has stimulated a series of experimental and theoretical works on scandium [16,31,[36][37][38].…”

Section: Introductionmentioning

confidence: 99%

First-principles investigation of Sc-III/IV under high pressure

et al. 2018

View full text Add to dashboard Cite

Using ab initio evolutionary structure prediction method in conjunction with density functional theory, we performed a systematic investigation on the structural transition of elemental scandium under pressure up to 250 GPa. Our prediction successfully reproduced several allotropes which have been reported in the previous literature, including the Sc-I, Sc-II and Sc-V. Moreover, we observed a series of energetically degenerate and geometrically similar structures at 110-195 GPa, which are likely to explain the unsolved phases III and IV reported by Akahama [Phys. Rev. Lett., 94, 19, 195503, (2005)]. A detailed comparison on powder X-ray diffraction pattern (PXRD) suggested that the Ccca-20 phase may account for the observed Sc-III, while Sc-IV is likely to be explained by a mixture of multiple energetically competing structures. We also used the candidate Sc-III structure as the model system to explore its superconducting behavior under pressures between 80-130 GPa. The predicted superconducting transition temperature Tc values are in satisfactory agreement with previous experimental results. *

show abstract

“…Previous computational studies have usually relied on the smallest possible commensurate approximants, although examples exist, for elementary and compound incommensurates, where the role of different host-guest ratios has been explored [35][36][37][38][39].…”

Section: Introductionmentioning

confidence: 99%

Structural and electronic properties of the alkali metal incommensurate phases

Woolman

Robinson

Marqués

et al. 2018

Phys. Rev. Materials

View full text Add to dashboard Cite

Under pressure, the alkali elements sodium, potassium, and rubidium adopt nonperiodic structures based on two incommensurate interpenetrating lattices. While all elements form the same "host" lattice, their "guest" lattices are all distinct. The physical mechanism that stabilizes these phases is not known, and detailed calculations are challenging due to the incommensurability of the lattices. Using a series of commensurate approximant structures, we tackle this issue using density functional theory calculations. In Na and K, the calculations prove accurate enough to reproduce not only the stability of the host-guest phases, but also the complicated pressure dependence of the host-guest ratio and the two guest-lattice transitions. We find Rb-IV to be metastable at all pressures, and suggest it is a high-temperature phase. The electronic structure of these materials is unique: they exhibit two distinct, coexisting types of electride behavior, with both fully localized pseudoanions and electrons localized in 1D wells in the host lattice, leading to low conductivity. While all phases feature pseudogaps in the electronic density of states, the perturbative free-electron picture applies to Na, but not to K and Rb, due to significant d-orbital population in the latter.

show abstract

Determination of the Structural Parameters of an Incommensurate Phase from First Principles: The Case of Sc-II

Cited by 17 publications

References 23 publications

Prediction of incommensurate crystal structure in Ca at high pressure

Prediction of incommensurate crystal structure in Ca at high pressure

First-principles investigation of Sc-III/IV under high pressure

Structural and electronic properties of the alkali metal incommensurate phases

Contact Info

Product

Resources

About