Structural and transport properties of (Bi,Pb)4Sr3Ca3Cu4−mFemOx (m=0–0.06) glasses: Precursors for high Tc superconductors

Abstract

Microstructure and transport properties (between 80–450 K) of the Fe doped as-quenched Bi3Pb1Sr3Ca3Cu4−mFemOx (m=0.0, 0.02, 0.04, 0.05, and 0.06) type multicomponent glassy precursors for high-temperature superconductors were first reported in this paper. It has been shown from x-ray diffraction, scanning electron microscopy, thermal analysis, density, and oxygen molar volume measurements that single phase homogeneous glasses are formed. Even with small addition of Fe, a large change of glass transition temperature (Tg) indicates appreciable change of glass network structure of the undoped (Bi,Pb)4Sr3Ca3Cu4Ox glass which is reflected in the properties of the corresponding high-temperature annealed glass termed as glass-ceramic (GC) samples. These GC samples are found to be superconductors. Addition of Fe is considered to break up some of the original Cu–O–Cu bonds forming some new Cu–O–Fe and Fe–O–Fe type bonds. A nonlinearity (increase) in the dc conductivity (σdc) of the as-quenched glass sample is observed around m=0.02. This increase of dc conductivity is ascribed to be due to the additional hopping between Fe2+ and Fe3+ which finally destroys superconductivity for m⩾0.06. This is also responsible for the nonlinear variation of activation energy of the Fe doped glass and hence change in the superconducting properties of the glass ceramics. The high temperature (above θD/2, θD being the Debye temperature) σdc data of the glasses were explained by considering small polaron hopping conduction mechanism. The dc conductivity of these glasses are found to follow Greaves’ variable range hopping model in the intermediate range of temperature. The polaron hopping model of Schnakenberg and Emin can predict the conductivity data in the high-temperature regime. All the Fe-doped glass ceramics showed superconducting transitions with Tc between 100 and 110 K. The corresponding zero resistance temperature, Tco which is maximum (79 K) for m=0, decreases consistently with increase of Fe-concentration and finally superconducting behavior is destroyed for m⩾0.06. This behavior is consistent with-pair breaking mechanism.

Non-adiabatic small polaron hopping in then= 3 Ruddlesden–Popper compound Ca4Mn3O10

“…Å similar to what has been found in other small polaron systems [54][55][56][57] . We, therefore, conclude that the calculated value of T 0 is consistent with a small polaron hopping mechanism.…”

“…Substituting n = 5.0 × 10 20 cm −3 (see below) into equation (4) yields N(E F ) ∼ 3.3 × 10 22 eV −1 cm −3 , which is comparable to the value calculated above from T 0 . Substituting the new value of N(E F ), scaled to 2D, into equation ( 3) results in a polaron radius of r p = α −1 ∼ 1.4 Å similar to that which has been found in other small polaron systems [56][57][58][59]. We therefore conclude that the calculated value of T 0 is consistent with a small polaron hopping mechanism.…”

“…The derived values of T 0 compare well with those reported for other transition metal oxides [46][47][48][49] Å similar to what has been found in other small polaron systems [54][55][56][57] . We, therefore, conclude that the calculated value of T 0 is consistent with a small polaron hopping mechanism.…”

Synthesis and Research of Critical Parameters of Bi-HTSC Ceramics Based on Glass Phase Obtained by IR Heating

“…According to [23,24], a significant loss of oxygen occurs during melting of the initial samples in the crucible, so that the ratio of Cu + /(Cu 1+ + Cu 2+ ) cations can reach a value of 0.7-0.8. Similar results with the reduction of Cu 2+ copper cations to Cu + when obtaining a melt in the crucible were observed in [24][25][26][27].…”

Synthesis of high-temperature superconducting ceramics in the Bi(Pb)-Sr-Ca-Cu-O system based on amorphous precursors

“…Among these methods, the traditional one is to obtain a melt in a crucible. For example, researchers [19] for the synthesis of the composition (Bi,Pb) 4 Sr 3 Ca 3 Cu 4-m Fe m O x (m=0-0.06) from an amorphous phase, melting was carried out in a platinum crucible and tempered by flaking between two massive plates. At the same time, the presence of low valence Fe + and Cu + cations was established, although Fe 2 O 3 oxides were used, CuO and melting was carried out in an oxidizing medium.…”