Crystal Structure and Electrical Property of Calcium under Very High Pressure

Nakamoto, Yuki; Yabuuchi, Takahiro; Matsuoka, Toshifumi; Shimizu, Katsuya; Takemura, Keiji

doi:10.1143/jpsjs.76sa.25

Cited by 15 publications

(10 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The samples were loaded into the DACs inside of a glovebox with an Ar atmosphere to avoid oxidization. Pressures were determined using the ruby fluorescence method or by measuring an X-ray powder diffraction of the sample and calculating the pressure using its known equation of state (8,24), especially for the high-pressure range (>40 GPa). The uncertainty of the pressure measurements was estimated to be ΔP ¼ AE0.4 GPa and ΔP ¼ AE1 GPa for the ruby pressure scale and the sample equation of state, respectively.…”

Section: Methodsmentioning

confidence: 99%

“…3 B and C for comparison; the β-tin structure I4 1 ∕amd phase can be viewed as a distortion of the sc structure. In the sc phase, Ca atom has six nearest neighbors at 2.728 Å occupying the octahedral site (24), while in the β-tin structure phase, the octahedron was distorted with four nearest neighbors at 2.754 Å and two next nearest neighbors at 2.831 Å.…”

mentioning

confidence: 99%

“…The most favorable path is through the Cmmm phase at low pressure. Yao et al (14) calcu- Typical full profile refinement of an in situ XRD pattern at 32.8 GPa, 6 K during decompression (A) and (B, C) comparison between crystal structures of β-tin-type tetragonal with I4 1 ∕amd symmetry at 32.8 GPa 6 K and sc at 32.8 GPa and room temperature (24). Rietveld refinements are performed using GSAS.…”

mentioning

confidence: 99%

See 2 more Smart Citations

Calcium with the β-tin structure at high pressure and low temperature

Ding

Yang

et al. 2012

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

View full text Add to dashboard Cite

Using synchrotron high-pressure X-ray diffraction at cryogenic temperatures, we have established the phase diagram for calcium up to 110 GPa and 5-300 K. We discovered the long-sought for theoretically predicted β-tin structured calcium with I4 1 ∕amd symmetry at 35 GPa in a s mall low-temperature range below 10 K, thus resolving the enigma of absence of this lowest enthalpy phase. The stability and relations among various distorted simple-cubic phases in the Ca-III region have also been examined and clarified over a wide range of high pressures and low temperatures.phase transition | structure distortion A t high pressures, calcium (Ca) not only displays very rich structural changes (1-5) but also holds the record for the highest superconducting critical temperature (T c ¼ 26 K) among elemental materials (5-7). Ca is currently one of the most studied elements under high pressure. A series of phase transitions have been observed in previous experiments. Under ambient conditions, Ca crystallizes in a face-centered cubic (fcc) structure (Ca-I). Increasing pressure at room temperature, Ca-I transforms to Ca-II with a body-centered cubic (bcc) structure at 20 GPa, to Ca-III with a simple cubic (sc) structure at 32 GPa (1, 2, 8), to Ca-IV (P4 1 2 1 2) at 119 GPa (3), to Ca-V (Cmca) at 143 GPa (3), to Ca-VI (Pnma) at 158 GPa (4), and to Ca-VII at 210 GPa (5). High-precision X-ray diffraction studies revealed rhombohedral (9) and orthorhombic distortions (4) of the sc structure. However, the distortions are very small. In this paper, we refer these slightly distorted sc structure generally as Ca-III for simplicity.Among the high-pressure phases, the Ca-III phase is particularly intriguing. The pressure-induced electronic transition from a normal metal to a superconductor occurs in the Ca-III phase region above 44 GPa (10, 11), and the T c increases with pressure from 2 K to 10 K within the Ca-III region (6). Ca-III is also a very active test case of modern theories and experiments, where a number of paradoxes arise (12-18). Based on density-functional theory (DFT) calculations, Ca-III with sc structure has imaginary phonon frequencies, indicating dynamic instability (19-21). On the other hand, high-pressure room temperature experiments confirmed that Ca-III adopts the nearly sc structure (8). To overcome this discrepancy, Teweldeberhan et al. (16) (17) provided a detailed analysis of ab initio molecular dynamics simulations that could account for the stability of the sc structure at room temperature. The remaining major discrepancy is that Yao et al. (14) and Oganov et al. (13) predicted that Ca with I4 1 ∕amd symmetry (β-tin structure) has a much lower zero-temperature enthalpy than sc, but in spite of many experimental efforts, the presumably more stable β-tin structured Ca has never been discovered. Here we report the search and discovery of the β-tin structured Ca and establish its stability range.To study the stability of sc Ca at ground state, Mao et al. (9) performed low-temperature experiments and observed an...

show abstract

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Calcium with the β-tin structure at high pressure and low temperature

Ding

Yang

et al. 2012

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

View full text Add to dashboard Cite

show abstract

“…A diffraction pattern of a single phase with no gasket peak was obtained for each phase [19]. Since the experimental condition is described in Ref.…”

mentioning

confidence: 99%

“…Since the experimental condition is described in Ref. [19], minimal information is given here. The beveled diamond anvils were used for pressure generation up to 158 GPa.…”

mentioning

confidence: 99%

Crystal Structures of Calcium IV and V under High Pressure

et al. 2008

Self Cite

View full text Add to dashboard Cite

High-pressure phases IV and V of calcium discovered in 2005 have the highest superconducting transition temperature of 25 K among all the elements; however, their crystal structures have not been determined. From the x-ray powder diffraction data, both Ca IV and V have been found to form unique and complex structures with a coordination number of 7. They were confirmed to be identical to the theoretical models that were recently predicted [Ishikawa, Phys. Rev. B 77 020101(R) (2008)].

show abstract