Recent developments in the emerging field of crystalline p-type transparent conducting oxide thin films

Quaternary rare earth transition metal arsenide oxides RTAsO (T=Fe, Ru, Co) with ZrCuSiAs type structure

A series of layered oxychalcogenide and oxypnictide solids is described that contain oxide layers separated by distinct layers, which contain the softer chalcogenide (S, Se, Te) or pnictide (P, As, Sb, Bi) anions. The relationships between the crystal structures adopted by these compounds are described, and the physical and chemical properties of these materials are related to the structures and the properties of the elements. The properties exhibited by the oxychalcogenide materials include semiconductor properties, for example, in LaOCuCh (Ch = chalcogenide) and derivatives, unusual magnetic properties exhibited by the class Sr2MO2Cu2−δS2 (M = Mn, Co, Ni), and redox properties exhibited by the materials Sr2MnO2Cu2m−0.5Sm+1 (m = 1−3) and Sr4Mn3O7.5Cu2Ch2 (Ch = S, Se). Recent results in the oxychalcogenide area are reviewed, and some new results on the intriguing series of compounds Sr2MO2Cu2−δS2 (M = Mn, Co, Ni) are reported. Oxypnictides have received less recent attention, but this is changing: a new f...

Structures, physical properties, and chemistry of layered oxychalcogenides and oxypnictides.

The discovery of a new superconductor, LaFeAsO(1-x)F(x) with a superconducting critical temperature,T(c), of 26 K in 2008, has quickly renewed interest in the exploration of iron-based superconductors. More than 70 new superconductors have been discovered within several months, with the highest T(c) of up to 55 K being observed in the SmFeAsO(1-x) compound. High T(c)s have previously only been observed in cuprates; these new iron-based superconductors have been added as second members of the high-T(c) family. The crystal structure of these compounds contains an almost 2D Fe-As layer formed by FeAs(4) tetrahedrons, which can be separated by an oxide or metal layer that provides extra electrons to the Fe-As layer, and the itinerant iron 3d electrons form an antiferromagnetic (AFM) order state in the undoped parent compounds at around 100-200 K. Superconductivity can be induced by carrier doping, which destroys the AFM ground state. In this Review, the most recent findings on and basic experimental facts about this class of high-T(c) materials will be presented, including the various superconducting structures, the synthesis methods, the physical properties of the parent compounds, the doping methods that could produce superconductivity, pressure effects, and the prospects for this new iron-based high-T(c) family.

Research and Prospects of Iron‐Based Superconductors

Among all the rare earth elements, Pr is known to behave as a singularity in the high-Tc families. When high-temperature cuprates are doped with Pr the superconductivity is quenched, and a metal insulator transition occurs. The origin of this behavior, being of fundamental interest, may also shed light on the mechanism of high-temperature superconductivity, since any reasonable theory for this mechanism should explain the behavior of the Pr-based system. The physical properties and the several theories which have been proposed to describe the anomalous behavior of Pr-doped systems in the normal and superconducting states are reviewed.

The question of Pr in HTSC

Synthesis and crystal structure of barium copper fluochalcogenides:[BaCuFQ (Q=S,Se)]

A Bi(Pb)2223/Ag multifilamentary tape was manufactured using the traditional PIT method. A series of the short samples cut from the tape were used to investigate the effect of low temperature-low oxygen pressure post-annealing on the critical current density of the samples. Two series of the air-sintered superconducting samples with the different intermediate pressing times and total sintering time were in situ post-annealed, respectively, under the reduced atmosphere taking the post-annealing temperature, time and oxygen partial pressure as variations. The results indicate that there are different effects of the post-annealing on the critical current density for the samples in the two series. Postannealing at the temperatures from 760 degrees C to 810 degrees C for a short time can improve the J(c) values up to 1.5-2.5 times for the samples in series 1, and the maximum value can be achieved at 780 degrees C, which makes the J(c)(A)/J(c)(B)-T (A: after the postannealing; B: before the post-annealing) curve present a single-peak form, whereas the J(c) values can be obviously improved up to 1.3-2.0 times at 820 degrees C and slightly improved at 780 degrees C for the samples in series 2, which makes the J(c)(A)/J(c)(B)-T curve present a double-peak form. XRD, SEM and ac susceptibility measurements indicate that the two different effects of the post-annealing, which closely depends on the sintering time of the samples before post-annealing, should be attributed to the two different phase transformations relating to the formation of(Bi,Pb)2212 and Bi2223, respectively, during the post-annealing. Formation of (Bi,Pb)2212 from Pb-poor Bi2212 and (Pb,Bi)(4-alpha)(Sr,Ca)(5-beta)CuOx (Pb451) at 780 degrees C for the samples with a shorter sintering time has an effect of improving the transition temperature of 2212 from 68-74 to 76-80 K and, therefore, overcomes the obstruction of the phase on the critical current at liquid nitrogen temperature and obviously improves the critical current density of the samples. The improvement of the J(c) values for the samples with a longer sintering time after being treated at 820 degrees C can be attributed to the formation of Bi2223 from Bi2212, Pb451 and (Sr,Ca)(14)Cu24Ox It seems that the effectiveness of post-annealing strongly depends on the sintering time of the samples before post-annealing: the formation of BiPb2212 at 780 degrees C needs a shorter time (relatively larger amount of Bi2212) in advance, whereas the formation of Bi2223 at 820 degrees C needs a longer time (decreased amount of Bi2212 and increased amount of (Sr,Ca)(14)Cu24Ox). Among the two phase transformations, the formation of Pb-enhanced Bi2212 at 780 degrees C seems to be of utmost importance and has a universal meaning for the manufacture of the Bi2223 tapes, which solves the intrinsic problem of the partial decomposition of Bi2223 during the furnace cooling and may present a new idea of improving the J(c) values through adjusting the transition temperature of the superconducting secondary phases besides the exhausted effort of making the Bi2223 single phase. The J(c) values after post-annealed at 780 degrees C for a short time for the samples with a shorter sintering time before the treatment can be comparable with that of the longer time sintered samples and the samples after post-annealed at 820 degrees C, which also reflects the importance of the transformation of Bi2212 into BiPb2212 on the critical current density of the tapes and makes the mechanism deserve to be further investigated. (C) 2000 Elsevier Science B.V. All rights reserved.

Influence of low temperature–low oxygen pressure post-annealing on critical current density of Bi(Pb)2223/Ag superconductors ☆

Infinite-layer Sr 1− x CuO 2 ( x = 0.0−0.3) samples have been prepared under high pressure. The average structure of the infinite- layer SrCuO 2 was refined by the Rietveld technique to be tetragonal with a = 3.9269 (2) A and c = 3.4346 (2) A . The infinite- layer Sr 1− x CuO 2 samples could be formed under high pressure for x = 0.0−0.3 in which the Sr deficiency was partially released by forming Cu rich impurity phase (s) such as CuO or Sr 14 Cu 24 O 41 . The microstructure of the Sr 1− x CuO 2 samples was characterized by high-resolution electron microscopy and Sr vacancies were not found to cluster into defect layers along the c -axis. The resistivity-temperature dependence of the Sr 1 − x CuO 2 ( x = 0.0−0.3) samples suggested that the Sr deficient infinite-layer phase might be electron-doped. An indication of superconductivity with T c onset = 60 K was observed in the Sr 1− x CuO 2 samples. When the samples were annealed in an oxidizing atmosphere, the indication of superconductivity remained at 60 K but the superconducting property was not improved remarkably. The origin of the superconductivity was discussed.

Structure and superconductivity in the infinite-layer Sr1−xCuO2 system prepared under high pressure

A low temperature-low oxygen pressure post-annealing method was introduced for a series of Bi(Pb)-2223/Ag multifilamentary meter-length rolled tapes manufactured using the different precursor powders. The universal effectiveness of the transformation of Bi2212 into BiPb2212 by the post-annealing on the improvement of the critical current density as reported earlier for the short pressed samples is examined. The results indicate that for most of the air-sintered tapes the critical current densities are improved up to 1.5-2.5 times after the short time post-annealing at 780 degrees C under 90% N-2-10% O-2 atmosphere and only a little exception with J(c) slightly decreased or increased after the treatment was observed. XRD and SEM measurements reveal that there are two different phase assemblages in the fully reacted tapes with J(c) increased (Bi2223 + 2212 + Bi3Pb0.6Sr2CaCu3Ox + (Pb, Bi)(4-alpha)(Sr, Ca)(5-beta)CuOx(Pb451) + (Sr, Ca)(14)Cu24Ox and Bi2223 + 2212 + Pb451 + (Sr, Ca)(14)Cu24Ox, respectively) due to the difference of Pb content in the precursor powders. Therefore, there have been different phase assemblage changes of Bi2223 + 2212*(increased) + Pb451(decreased) + (Sr, Ca)(14)Cu24Ox and Bi2223 + 2212* (increased) + (Sr, Ca)(24)Cu24Ox, respectively, after the post-annealing. An improved grain alignment and colony boundary can also be observed besides the decrease of the non-superconducting impurities and the increase of 2212. XRD measurements also indicate that some undesired reactions may happen for the slightly decreased or increased tapes during the post-annealing, which should be responsible for the ineffectiveness of the treatment in these tapes. Ac susceptibility measurements for the J(c) improved samples show an obvious increase of the transition temperature of 2212 from 68 to 76 K after the post-annealing. It can be concluded that the low temperature-low oxygen pressure post-annealing method is an effective means considering the eliminating of the weak links. The mechanism of the treatment can be determined as the overcoming of the main weak links of Pb-poor Bi2212 by the transformation of this lower T-c phase (68 K) to the higher T-c phase (76 K) cooperated simultaneously with the elimination of the weak links of the non-superconducting impurities during the transformation. This mechanism, which concentrates on the increase of the transition temperature of the low T-c phase instead of the exhausted efforts of making the single Bi2223 phase, may imply a shorter sintering time and a decreased number of the intermediate deformation. Therefore, it may present some new ideas on the manufacture of the Bi2223 tapes operated at the liquid nitrogen temperature, which makes the method noteworthy and further investigated. (C) 2000 Elsevier Science B.V. All rights reserved.

Phase transformation and critical current density of (Bi, Pb)-2223/Ag superconducting tapes by a low temperature–low oxygen pressure post-annealing method

The Rutherford backscattering/channelling technique of 2.1 MeV He ions has been used to study the damage distribution in Si irradiated with 1.0 MeV Ti ions to a dose of 5 x 10(14) ions cn-2 under 7-degrees and 60-degrees incidence. A dechannelling analysis of multiple scattering has been made. The longitudinal damage straggling and lateral damage spread are estimated. The values obtained are compared with transport of ions in matter. The results show that the differences between experimental and calculated values for longitudinal damage straggling and the lateral damage spread are 25% and 28%, respectively. Also, it is observed that the damage distribution shape under 60-degrees irradiation is found in good qualitative agreement with an earlier simulation.

F. Wu

Papers

Synthesis and crystal structure of barium copper fluochalcogenides:[BaCuFQ (Q=S,Se)]

Influence of low temperature–low oxygen pressure post-annealing on critical current density of Bi(Pb)2223/Ag superconductors ☆

Structure and superconductivity in the infinite-layer Sr1−xCuO2 system prepared under high pressure

Phase transformation and critical current density of (Bi, Pb)-2223/Ag superconducting tapes by a low temperature–low oxygen pressure post-annealing method

Structural and superconducting properties of the infinite-layer (Sr, Ca)1−yCuO2 prepared under high pressure