Crystal structure and superconductivity of a high-pressure phase of CaSi2

McWhan, D. B.; Compton, V.B.; Silverman, M. S.; Soulen, J. R.

doi:10.1016/0022-5088(67)90073-2

Cited by 30 publications

(11 citation statements)

References 6 publications

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“…At high pressures, CaSi 2 shows polymorphic behaviour and forms high-pressure modifications with crystal structures of the ThSi 2 type (4 GPa and 1270 K to 8.7 GPa and 1770 K [21][22][23][24][25]), with trigonal symmetry (9 GPaoPo16 GPa at ambient temperature [26,27]) and with an AlB 2 -like pattern (P416 GPa and ambient temperature [26,27]). …”

Section: Article In Pressmentioning

confidence: 99%

High-pressure synthesis of the electron-excess compound CaSi₆

Wosylus

Prots

Burkhardt

et al. 2007

Science and Technology of Advanced Materials

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The binary phase CaSi 6 is prepared at a pressure of 10(1) GPa and a temperature of 1520(150) K. X-ray single-crystal structure refinements and powder diffraction data of quenched samples reveal that the compound crystallizes in the orthorhombic crystal system (space group Cmcm, a ¼ 4.4953(5) Å , b ¼ 10.078(1) Å , c ¼ 11.469(1) Å ). At ambient pressure, exothermic decomposition into CaSi 2 and Si at 737(5) K indicates that the compound is a metastable high-pressure phase. Physical property measurements reveal that the new hexasilicide is diamagnetic and a bad metallic conductor, with resistivity rE900 mO cm at 300 K. r

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Section: Article In Pressmentioning

confidence: 99%

High-pressure synthesis of the electron-excess compound CaSi₆

Wosylus

Prots

Burkhardt

et al. 2007

Science and Technology of Advanced Materials

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“…8 A high-pressure phase 9 with ␣-ThSi 2 type tetragonal structure ͓Fig. 1͑c͔͒ formed by interconnected sp 2 silicon atoms that rotate alternatively in the c-axis direction has been found to be superconducting with T c ϭ1.58 K. 10 In this report we describe the effects of high pressures ͑р22 GPa͒ on the behavior of the resistivity of these two CaSi 2 phases. We show that under pressure this system undergoes a series of phase transitions which finally develop superconductivity with one of the highest transition temperatures known for a silicon based compound, i.e., T c ϭ14 K.…”

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confidence: 96%

“…ac susceptibility measurements performed on this sample showed a sharp superconducting transition at 1.51 K, in agreement with what was previously reported. 10 Samples were then cut and polished down to the size necessary for measurements under pressure, namely 0.05ϫ0.05ϫ0.3 mm 3 .…”

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Superconducting high pressureCaSi2phase withTcup to 14 K

et al. 2000

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We have studied the occurrence of superconductivity under pressure in the CaSi 2 family of compounds, namely the semimetallic trigonal phase and the ␣-ThSi 2 -type tetragonal one. Although only the latter is superconducting (T c ϭ1.56 K) at ambient pressure, starting from the trigonal phase and applying high pressure ͑Ͼ12 GPa͒ we have found a new superconducting phase with T c onset ϳ14 K, among the highest ever found in silicon based materials.Silicon and Si-based compounds are in general extensively studied as they are at the base of electronics and microdevices. Although intriguing and of practical interest, the appearance of superconductivity in these materials has not been so exhaustively explored. Yet the different bonding possibilities of silicon give rise to slightly different structural phases that can differ very much in their physical behavior. In 1985, the sp 2 simple hexagonal phase of pure Si was predicted and then found to be superconducting with transition temperature T c ϭ8.2 K under high pressure ͑15 GPa͒ by Chang and co-workers. 1 Similarly to C 60 fullerenes, the Si 20 fullerenes can be doped by alkali-metal atoms, when linked together through their dangling sp 3 bonds to form the structure of the clathrate (Na, Ba) x Si 46 , a superconductor with T c ϭ4 K. 2 Some silicides (NbSi 2 , TaSi 2 ) are also known to be superconductors 3 with typical T c 's of the order of 1 K, with the exception of the A-15 compounds, such as V 3 Si (T c ϭ17 K), where the linear chain bands of vanadium are at the origin of superconductivity. 4 More recently, the highpressure EuGe 2 -type phase ͓Fig. 1͑c͒, named as h1 in the following͔ of BaSi 2 , built by planes of boat-formed sp 3 silicon hexagons held together by hexagonal planes of calcium atoms, was found to be superconducting with T c onset ϭ6 K. 5 Pressure can indeed be a very useful variable allowing a gradual change of the lattice parameter of a particular silicide and forcing it to change to new configurations more favorable for superconductivity. As shown by the experiments on elementary silicon, in situ measurements using pressures in the range of 10 GPa may be adequate to scan a succession of interesting phases. Plausible candidates are large volume per unit formula silicides such as CaSi 2 . At ambient pressure CaSi 2 has a trigonal structure ͓also labeled TR6 in the following͔ 6 ͓Fig. 1͑a͔͒. In this form it is a semimetal 7 with an electrical resistivity that follows the conventional BlochGrüneisen temperature dependence and it is not superconducting down to 30 mK. 8 A high-pressure phase 9 with ␣-ThSi 2 type tetragonal structure ͓Fig. 1͑c͔͒ formed by interconnected sp 2 silicon atoms that rotate alternatively in the c-axis direction has been found to be superconducting with T c ϭ1.58 K. 10 In this report we describe the effects of high pressures ͑р22 GPa͒ on the behavior of the resistivity of these two CaSi 2 phases. We show that under pressure this system undergoes a series of phase transitions which finally develop superconductivity with one of the ...

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“…A high-pressure phase of CaSi 2 , which appears above 16 GPa, has an AlB 2 -like structure in which Si atoms form slightly corrugated honeycomb layers [7]. This phase of CaSi 2 is superconductive, with a T C of 14 K at such pressures [8], while the ambient phase is not [9]. This high-pressure phase cannot be quenched at ambient conditions.…”

Section: Introductionmentioning

confidence: 99%

Superconductivity of MI(MII0.5,Si0.5)2 (MI=Sr and Ba, MII=Al and Ga), ternary silicides with the AlB2-type structure

Imai

Nishida

Kimura

et al. 2002

Physica C: Superconductivity

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Ternary silicides M I (M II0.5 , Si 0.5 ) 2 (M I =Sr and Ba, M II =Al and Ga) were prepared by Ar arc melting. Powder X-ray diffraction indicates that they have the AlB 2 -type structure, in which Si and M II atoms are arranged in honeycomb layers and M I atoms are intercalated between them. Electrical resistivity and dc magnetization measurements revealed that Sr(Al 0.5 , Si 0.5 ) 2 is superconductive, with a critical temperature for superconductivity (T C ) of 4.2 K, while Ba(Al 0.5 , Si 0.5 ) 2 is not at temperatures ranging above 2.0 K. Sr(Ga 0.5 , Si 0.5 ) 2 and Ba(Ga 0.5 , Si 0.5 ) 2 are also superconductors, with T C s of 5.1 and 3.3 K, respectively.

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Crystal structure and superconductivity of a high-pressure phase of CaSi2

Cited by 30 publications

References 6 publications

High-pressure synthesis of the electron-excess compound CaSi₆

High-pressure synthesis of the electron-excess compound CaSi₆

Superconducting high pressureCaSi2phase withTcup to 14 K

Superconductivity of MI(MII0.5,Si0.5)2 (MI=Sr and Ba, MII=Al and Ga), ternary silicides with the AlB2-type structure

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Crystal structure and superconductivity of a high-pressure phase of CaSi2

Cited by 30 publications

References 6 publications

High-pressure synthesis of the electron-excess compound CaSi6

High-pressure synthesis of the electron-excess compound CaSi6

Superconducting high pressureCaSi2phase withTcup to 14 K

Superconductivity of MI(MII0.5,Si0.5)2 (MI=Sr and Ba, MII=Al and Ga), ternary silicides with the AlB2-type structure

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High-pressure synthesis of the electron-excess compound CaSi₆

High-pressure synthesis of the electron-excess compound CaSi₆