Pr4Fe2As2Te

Abstract

We report crystal growth at high pressure, structure determination, and magnetic and transport studies of an oxypnictide superconductor Pr 4 Fe 2 As 2 Te 1−x O 4 . Its structure resembles the known 1111 phase except for the considerably larger c lattice constant and intercalated tellurium atoms and it crystallizes in a tetragonal lattice [a = 4.0165(2)Å, c = 29.8572(16)Å, and space group I 4/mmm (no. 139)]. The electrical resistivity ρ(T) and magnetization measurement show a transition at T c ≈ 25 K. The lower (H c1 ) and upper (H c2 ) critical fields are 2 mT and 6.5 T, respectively. The Ginzburg-Landau parameter of κ ≈ 80 places this compound in the family of strong type-II superconductors.The layered d-metal pnictide and pnictide oxides (oxypnictides) have been intensively studied in recent years (see the review article 1 and references therein). This family consists of anti-fluorite-type M 2 P 2 (M is a transition metal and P a pnictogen) layers alternating for some representatives with fluorite-type L 2 O 2 layers (where L is a lanthanide). There are more than ten known structural types of this kind. 2,3 Some of them reveal superconductivity with a critical temperature T c up to 58.1 K. 4 The "new generation of high-T c materials" 5 provides a broad research area because of the huge variability in chemical composition with a potential to form new structural types. 1,3,6 Some of these compounds, like SmFeAs(O,F), due to the optimal combination of high isotropic critical current densities and the relatively high T c , could be considered as materials which meet requirements for possible applications. 7 Here we report on another compound of the layered d-metal oxypnictide superconductors, Pr 4 Fe 2 As 2 Te 1−x O 4 , its crystal structure and basic physical properties such as T c , dc resistivity, lower and upper critical fields, and Ginzburg-Landau parameters. For its synthesis a mixture of chemicals PrAs, PrTe, and FeO in molar proportion 0.9:0.1:1 was thoroughly ground in a malachite mortar and pressed into a pellet inside a glovebox in argon gas. The pellet was annealed at 1050 • C for 7 days in an Al 2 O 3 crucible in a sealed quartz ampoule filled with Ar gas (≈0.2 atm). After that it was quenched in cold water. This precursor was used for crystal growth at high pressure (3 GPa) in NaCl/KCl flux employing a high-pressure cubic anvil system. The temperature was raised to 1500 • C in 1 h and then kept constant for 60 h, followed by cooling (45 • C/h) to 1050 • C and cooling in 1 h to room temperature. The flux was dissolved in water. The crystals of platelike shape were selected from the remaining mixture.Single-crystal x-ray diffraction was performed on a Bruker diffractometer equipped with a CCD detector. Data reduction and multiscan absorption correction were done using APEX2 (Ref. 8) and SAINT (Ref. 9) software. The crystal structure was determined by a direct method and refined on F 2 , employing the programs SHELXS-97 (Ref. 10) and . The lattice parameters were determined as a = 4.0165(2)Å and c = 29.8...

Upper critical field, pressure-dependent superconductivity and electronic anisotropy of Sm4Fe2As2Te1−xO4−yFy

“…However, it's unlikely that intrinsic Josephson junction effect could occur in Sm4Fe2As2Te1-xO4-yFy because of the short Fe2As2 inter-layer distance ( ) compared to the out-of-plane coherence length ( 0.7 c  ). The ab plane resistivity decreases with lowering temperature and a mild upturn is observed just above Tc, exactly as observed in the single crystal from which the lamella was extracted [2]. This upturn could come from slight admixture of the out-of-plane resistivity which gives a different appearance of ab  than in figure 2.…”

“…Details regarding the crystals growth and their characterization are described elsewhere [1,2]. To measure electrical resistivity (  ) a standard fourpoint configuration was adopted.…”

“…The presence of tellurium vacancies is thought to be responsible for superconductivity occurring at 25 K in L4Fe2As2Te1-xO4 samples. Here we present a systematic and comprehensive study of the electronic and magnetic properties of Sm4Fe2As2Te1-xO1-yFy which displays Tc=40 K upon optimum electron doping by fluorine substitution [2]. We report the upper critical field, pressure-dependent resistivity and direct measurement of the electronic anisotropy of Sm4Fe2As2Te0.72O2.8F1.2.…”

“…1 . These compounds present critical temperatures (Tc) up to 46 K upon substitution of the rare earth element and optimum fluorine doping.…”

Co and Mn doping effect in polycrystalline (Ca,La) and (Ca,Pr)FeAs2superconductors

“…Ba 2 Ti 2 Fe 2 As 4 O [7] ), and RE 4 TeO 4 layers (ex. Pr 4 Fe 2 As 2 TeO 4 [8] ), have been successively found.…”