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Superconductivity of molybdenum phosphides prepared at high pressure
Physica B 281&282 (2000) 1024}1025
Superconductivity of molybdenum phosphides prepared at high pressure Ichimin Shirotani!,*, Isamu Kaneko!, Mitsuru Takaya!, Chihiro Sekine!, Takehiko Yagi" !Faculty of Engineering, Muroran Institute of Technology, 27-1, Mizumoto, Muroran-shi 050-8585, Japan "The Institute for Solid State Physics, University of Tokyo, Tokyo 106-8666, Japan
Abstract Binary molybdenum phosphides Mo P, Mo P and Mo P have been prepared at high temperatures and high 3 8 5 4 3 pressures. The resistivity of the phosphides decreases with decreasing temperature and sharply drops at low temperatures. The superconductivity is found at around 7 K for Mo P, 5.8 K for Mo P and 3 K for Mo P . The ¹ of the 3 8 5 4 3 # binary molybdenum phosphides decreases with decreasing density. The compounds Mo P and Mo P are new 8 5 4 3 superconductors. ( 2000 Elsevier Science B.V. All rights reserved. Keywords: Superconductivity; Molybdenum phosphide; High pressure
1. Introduction A superconductivity of Mo P has been found at low 3 temperatures [1,2]. Mo P crystallizes with the a-V S3 3 type structure [3]. The crystal structure of binary molybdenum phosphides Mo P and Mo P has also been 8 5 4 3 determined [4,5]. Electrical and magnetic properties of these molybdenum phosphides has not been studied in detail. We have prepared the binary molybdenum phosphides at high temperatures and high pressures. Mo P, Mo P 3 8 5 and Mo P show the superconducting transition at 4 3 around 7, 5.8 and 3 K, respectively. Mo P and Mo P 8 5 4 3 are new superconductors.
2. Experimental Using a wedge-type cubic-anvil high-pressure apparatus [6], binary molybdenum phosphides were prepared by the reaction of stoichiometric molybdenum and red
* Corresponding author. Tel.: #81-143-46-5544; fax: #81143-46-5501. E-mail address: [email protected] (I. Shirotani)
phosphorus powders at around 4 GPa, and at temperatures between 12003C and 17003C . The sample assembly for the preparation of the phosphides is similar to that used for the synthesis of black phosphorus [7].
3. Results and discussion Fig. 1 shows the resistivity of Mo P at low temper3 atures. The resistivity decreases with decreasing temperature, and sharply drops at around 7 K. Fig. 2 shows the temperature dependence of the DC susceptibility measured in an applied magnetic "eld of 5 Oe for Mo P. The 3 susceptibility of the phosphide sharply decreases at around 6 K. The sample cooled in zero "eld shows a magnetic shielding equal to approximately 100% of that expected for perfect diamagnetism. The existence of hysteresis between zero-"eld cooling (ZFC) and "eld cooling (FC) indicates that the phosphide is a type-II superconductor. Fig. 3 shows the resistivity versus temperature curve of Mo P at low temperatures. The resistivity of the 8 5 phosphide is higher than that of Mo P. However, the 3 temperature dependence of the resistivity of Mo P is 8 5 similar to the resistivity versus temperature curve of Mo P. The resistivity of Mo P sharply drops at around 3 8 5
0921-4526/00/$ - see front matter ( 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 0 8 9 4 - 7
I. Shirotani et al. / Physica B 281&282 (2000) 1024}1025
1025
Table 1 The ¹ , the density, the shortest Mo}Mo and Mo}P distances # in four binary molybdenum phosphides Compound ¹ (K) Density Shortest Mo}Mo Shortest Mo}P # (g/cm3) distances (As ) distances (As ) Mo P 3 Mo P 8 5 Mo P 4 3 MoP
Fig. 1. Resistivity versus temperature curve of Mo P at low 3 temperatures.
Fig. 2. Magnetic susceptibility measured in an applied magnetic "eld of 5 Oe for Mo P at low temperatures. 3
7 5.8 3 (1
9.098 8.251 7.861 6.360
2.565 2.900 2.839 3.191
2.437 2.331 2.348 2.451
The ¹ , the density, the shortest Mo}Mo and Mo}P # distances for four binary molybdenum phosphides are summarized in Table 1. The ¹ of Mo P with the largest # 3 density is highest among the binary molybdenum phosphides. The molybdenum monophosphide MoP dose not show the superconducting transition down to 1 K [2]. The density of MoP with the WC-type structure [8] is smallest as shown in Table 1. Thus, the ¹ of the # binary molybdenum phosphides decreases with decreasing density. The shortest Mo}Mo distance ("2.565 As ) in Mo P is much shorter than the sum of the atomic radius 3 of Mo ("1.39 As ). This distance is shortest among the binary molybdenum phosphides. The molybdenum atoms strongly bind in Mo P. The strong metal}metal 3 bond plays an important role for the enhancement of the superconductivity in the binary molybdenum phosphides. On the other hand, the shortest Mo}P distances in four binary molybdenum phosphides are shorter than the sum of the atomic radius of molybdenum ("1.39 As ) and the covalent radius of phosphorus ("1.10 As ). There is the strong covalent bond character between Mo and P atoms in these phosphides. We have prepared binary nickel phosphides at high temperatures and high pressures. These phosphides behave like metals, but do not show the superconductivity down to 2 K [6]. The Ni}P distances in the phosphides are shorter than the sum of the atomic radius of nickel ("1.24 As ) and the covalent radius of phosphorus ("1.10 As ). These results suggest that the metallic character in binary molybdenum and nickel phosphides arises from the strong interaction between metal and phosphorus atoms.
References
Fig. 3. Electrical resistivity of Mo P at low temperatures. 8 5
5.8 K. The DC magnetic susceptibility of the phosphide rapidly decreases at around 5 K. The superconducting transition of Mo P with the orthorhombic structure 4 3 (space group Pnma) is observed at around 3 K.
[1] [2] [3] [4] [5] [6] [7] [8]
B.T. Matthias et al., Phys. Rev. 93 (1954) 1415. R.D. Blaugher et al., J. Phys. Chem. Solids. 26 (1965) 2037. B. Sellberg, S. Rundquvist, Acta Chem. Scand. 19 (1965) 760. T. Johnsson, Acta Chem. Scand. 26 (1972) 365. S. Rundquvist, Acta Chem. Scand. 19 (1965) 393. I. Shirotani et al., Jpn. J. Appl. Phys. 32}3 (Suppl.) (1993) 294. I. Shirotani, Mol. Cryst. Liq. Cryst. 86 (1982) 1943. S. Rundquvist, T. LundstroK m, Acta Chem. Scand. 17 (1963) 37.
Superconductivity of molybdenum phosphides prepared at high pressure Ichimin Shirotani!,*, Isamu Kaneko!, Mitsuru Takaya!, Chihiro Sekine!, Takehiko Yagi" !Faculty of Engineering, Muroran Institute of Technology, 27-1, Mizumoto, Muroran-shi 050-8585, Japan "The Institute for Solid State Physics, University of Tokyo, Tokyo 106-8666, Japan
Abstract Binary molybdenum phosphides Mo P, Mo P and Mo P have been prepared at high temperatures and high 3 8 5 4 3 pressures. The resistivity of the phosphides decreases with decreasing temperature and sharply drops at low temperatures. The superconductivity is found at around 7 K for Mo P, 5.8 K for Mo P and 3 K for Mo P . The ¹ of the 3 8 5 4 3 # binary molybdenum phosphides decreases with decreasing density. The compounds Mo P and Mo P are new 8 5 4 3 superconductors. ( 2000 Elsevier Science B.V. All rights reserved. Keywords: Superconductivity; Molybdenum phosphide; High pressure
1. Introduction A superconductivity of Mo P has been found at low 3 temperatures [1,2]. Mo P crystallizes with the a-V S3 3 type structure [3]. The crystal structure of binary molybdenum phosphides Mo P and Mo P has also been 8 5 4 3 determined [4,5]. Electrical and magnetic properties of these molybdenum phosphides has not been studied in detail. We have prepared the binary molybdenum phosphides at high temperatures and high pressures. Mo P, Mo P 3 8 5 and Mo P show the superconducting transition at 4 3 around 7, 5.8 and 3 K, respectively. Mo P and Mo P 8 5 4 3 are new superconductors.
2. Experimental Using a wedge-type cubic-anvil high-pressure apparatus [6], binary molybdenum phosphides were prepared by the reaction of stoichiometric molybdenum and red
* Corresponding author. Tel.: #81-143-46-5544; fax: #81143-46-5501. E-mail address: [email protected] (I. Shirotani)
phosphorus powders at around 4 GPa, and at temperatures between 12003C and 17003C . The sample assembly for the preparation of the phosphides is similar to that used for the synthesis of black phosphorus [7].
3. Results and discussion Fig. 1 shows the resistivity of Mo P at low temper3 atures. The resistivity decreases with decreasing temperature, and sharply drops at around 7 K. Fig. 2 shows the temperature dependence of the DC susceptibility measured in an applied magnetic "eld of 5 Oe for Mo P. The 3 susceptibility of the phosphide sharply decreases at around 6 K. The sample cooled in zero "eld shows a magnetic shielding equal to approximately 100% of that expected for perfect diamagnetism. The existence of hysteresis between zero-"eld cooling (ZFC) and "eld cooling (FC) indicates that the phosphide is a type-II superconductor. Fig. 3 shows the resistivity versus temperature curve of Mo P at low temperatures. The resistivity of the 8 5 phosphide is higher than that of Mo P. However, the 3 temperature dependence of the resistivity of Mo P is 8 5 similar to the resistivity versus temperature curve of Mo P. The resistivity of Mo P sharply drops at around 3 8 5
0921-4526/00/$ - see front matter ( 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 0 8 9 4 - 7
I. Shirotani et al. / Physica B 281&282 (2000) 1024}1025
1025
Table 1 The ¹ , the density, the shortest Mo}Mo and Mo}P distances # in four binary molybdenum phosphides Compound ¹ (K) Density Shortest Mo}Mo Shortest Mo}P # (g/cm3) distances (As ) distances (As ) Mo P 3 Mo P 8 5 Mo P 4 3 MoP
Fig. 1. Resistivity versus temperature curve of Mo P at low 3 temperatures.
Fig. 2. Magnetic susceptibility measured in an applied magnetic "eld of 5 Oe for Mo P at low temperatures. 3
7 5.8 3 (1
9.098 8.251 7.861 6.360
2.565 2.900 2.839 3.191
2.437 2.331 2.348 2.451
The ¹ , the density, the shortest Mo}Mo and Mo}P # distances for four binary molybdenum phosphides are summarized in Table 1. The ¹ of Mo P with the largest # 3 density is highest among the binary molybdenum phosphides. The molybdenum monophosphide MoP dose not show the superconducting transition down to 1 K [2]. The density of MoP with the WC-type structure [8] is smallest as shown in Table 1. Thus, the ¹ of the # binary molybdenum phosphides decreases with decreasing density. The shortest Mo}Mo distance ("2.565 As ) in Mo P is much shorter than the sum of the atomic radius 3 of Mo ("1.39 As ). This distance is shortest among the binary molybdenum phosphides. The molybdenum atoms strongly bind in Mo P. The strong metal}metal 3 bond plays an important role for the enhancement of the superconductivity in the binary molybdenum phosphides. On the other hand, the shortest Mo}P distances in four binary molybdenum phosphides are shorter than the sum of the atomic radius of molybdenum ("1.39 As ) and the covalent radius of phosphorus ("1.10 As ). There is the strong covalent bond character between Mo and P atoms in these phosphides. We have prepared binary nickel phosphides at high temperatures and high pressures. These phosphides behave like metals, but do not show the superconductivity down to 2 K [6]. The Ni}P distances in the phosphides are shorter than the sum of the atomic radius of nickel ("1.24 As ) and the covalent radius of phosphorus ("1.10 As ). These results suggest that the metallic character in binary molybdenum and nickel phosphides arises from the strong interaction between metal and phosphorus atoms.
References
Fig. 3. Electrical resistivity of Mo P at low temperatures. 8 5
5.8 K. The DC magnetic susceptibility of the phosphide rapidly decreases at around 5 K. The superconducting transition of Mo P with the orthorhombic structure 4 3 (space group Pnma) is observed at around 3 K.
[1] [2] [3] [4] [5] [6] [7] [8]
B.T. Matthias et al., Phys. Rev. 93 (1954) 1415. R.D. Blaugher et al., J. Phys. Chem. Solids. 26 (1965) 2037. B. Sellberg, S. Rundquvist, Acta Chem. Scand. 19 (1965) 760. T. Johnsson, Acta Chem. Scand. 26 (1972) 365. S. Rundquvist, Acta Chem. Scand. 19 (1965) 393. I. Shirotani et al., Jpn. J. Appl. Phys. 32}3 (Suppl.) (1993) 294. I. Shirotani, Mol. Cryst. Liq. Cryst. 86 (1982) 1943. S. Rundquvist, T. LundstroK m, Acta Chem. Scand. 17 (1963) 37.