Evidence of non‐adiabatic small polaron hopping conduction in Bi_0.1A_0.9MnO₃ (A = Ca, Sr, Pb)

Abstract

A detailed study of the electrical transport properties of semiconducting perovskites Bi 0.1 A 0.9 MnO 3 (A = Ca, Sr, Pb of increasing ionic radius r i ) have been made over a wide range of temperature 80 -375 K. XRD studies indicate a change of structural differences with change of ionic radius r i of A. The dc conductivity of the Sr-and Pb-doped samples with larger r i is much lower than that of the Ca-doped sample of smaller r i . Unlike the Sr-and Pb-doped samples, little negative magnetoresistance is also observed in the Ca-doped sample (below 115 K at 1.5 T field). The resistivity data below θ D /2 (θ D is the Debye temperature) are fitted well with the Mott's variable range hopping (VRH) model, whereas the nearestneighbour small polaron hopping mechanism satisfactorily fitted the high-temperature (above θ D /2 ≈ 200 K) conductivity data. The condition of the non-adiabatic small polaron hopping mechanism is valid for all the samples. The estimated electron-phonon interaction constant γ p (= 2W H /hν ph ) of the highly resistive Sr-and Pb-doped samples are much higher (ӷ4) than those of the low-resistive Ca-doped oxide sample (≈4). Large values of γ p destroy spin ordering in the Sr-and Pb-doped samples, while for the lower value of γ p in the Ca-doped sample spin ordering favours high conductivity and show a negative magnetoresistance (only in the low-temperature region). Low-temperature (T < θ D /2) frequency-dependent ac conductivity data indicate that the conduction mechanism in the highly resistive Sr-and Pb-doped samples is primarily due to hopping of Anderson-localized charge carriers.

Doped Pr0.7−xBixSr0.3MnO3 manganite: A structural, electrical and magnetic effect

“…There is a decrease in volume similar as reported by W. Boujelben et al [1]. Although Bi 3+ (1.17 Å) ion has larger ionic radii than Pr 3+ (1.126 Å) ion with coordination VIII, hence increase in volume may be ascribed due to the presence of magnetic polarons originated as a result of the competing behavior of larger ionic radii generated ferromagnetic-DE and charge order state of the end compound BiSrMnO 3 compound [17][18][19]. The calculated lattice parameters (a, b and c) and unit cell volume with fitting reliability parameter are listed in Table 1.…”

“…Larger ionic radii of Bi 3+ ion supports DE conduction mechanism, hence resistivity decrease for x < 0.20 doping concentration. For x > 0.20, the charge ordered state of end Bi 1−x Sr x MnO 3 (BSMO) compound starts dominating [18,19]. As a result competition between DE and charge ordered state, resistivity increases and a peak generates in low temperature regime [20].…”

Electric relaxation and Mn3+/Mn4+ charge transfer in Fe-doped Bi12MnO20–BiMn2O5 structural self-composite

“…The Mö ssbauer spectroscopy study confirmed the variance in the surrounding of Fe [23,27,28,38,39]. It would be noticed that two relaxation processes occurred also in the non-doped Bi 12 MnO 20 -BiMn 2 O 5 self-composite [12].…”

“…It should be noted that several compounds containing Mn ions show polaronic conduction [12,23,24,27,28,38,39]. There are two models of small polaron conductivity, which include the potential energy landscape determined by the degree of crystal lattice disorder [25,26].…”

“…valence in several bismuth manganite compounds was related not only to magnetic ordering but also to the small polaron mechanism of conductivity [9,23]. Moreover, in case of increased structural disorder, the variable range hopping (VRH) of small polaron can manifest in lowtemperature ranges [24][25][26][27][28]. Doping with Fe ions can serve as a probe for determination of the local crystal lattice symmetry or environment of the ions in the Fe/Mn sublattice.…”