Thermopower studies of Pr_0.67D_0.33MnO₃manganite system

Abstract

With a view to explaining the structural and electrical transport behaviour of some rare earth manganites, having the general formula Pr0.67D0.33MnO3 (D = Ca, Sr, Pb and Ba), a systematic investigation of the electrical resistivity, thermopower and magnetic properties has been undertaken. These materials were prepared using the citrate–gel route by sintering at 900 °C. All the materials were characterized by x-ray diffraction, scanning electron microscopy, etc measurements. The x-ray data were analysed using the Rietveld method and the variation of various parameters involved in the process as explained. The average crystallite size of the materials has been estimated using the peak broadening method, while TC and TP values were determined from ac magnetic susceptibility and electrical resistivity measurements, respectively. Finally, the magnetoresistance (MR) measurements were also carried out over a magnetic field of 1–7 T and the data clearly exhibit the extrinsic MR in ferromagnetic metallic region.The influence of average A-site cation radius ⟨rA⟩ and cation mismatch parameter σ2 on thermoelectric power (TEP), MR, electrical and magnetic transitions has been analysed. The TEP data at low temperatures (T < TP) have been analysed by considering the magnon concepts, while the high temperature (T > TP) data were explained by the Mott's small polaron conduction mechanism. The effects of ⟨rA⟩ and σ2 on polaron activation and hopping energies were also studied systematically.

Theoretical study of magnetotransport properties of colossal magnetoresistive manganites (Re1−xAxMnO3): A variational treatment

“…This large value of Q(T) arising from hole localization may occur due to the narrowing of e g band. This behavior of Q(T) agrees qualitatively with some CMR compounds such as La 0.67 Ca 0.33 MnO 3 [23] and La 5/8 À y Pr y Ca 3/8 MnO 3 with y ¼0.25, 0.35 and 0.42 [24]. Fig.…”

Role of iso-electronic Ru5+ in thermal transport behavior of YMn1-xRuxO3 compounds

“…Similar to the electrical conduction, several factors like impurity, band structure, electron-electron, electron-magnon scattering, etc., affect thermoelectric properties. Though the picture is still not very clear, it is quite justified to assume that the electrical conduction and thermoelectric power are closely related to the similar mechanism and the decreasing TEP with incremental Ru concentrations further supports the consensus of induced FM and metallicity [32][33].…”

Influence of sintering temperature and oxygen stoichiometry on electrical transport properties of La0.67Na0.33MnO3 manganite

“…In a manner similar to the scattering Table 3 The fitting parameters of thermoelectric power data in La0.67Na0.33MnO3 manganites of phonons resulting in phonon drag effects, the electron magnon interaction produces a magnon drag effect. As the magnon drag effect is approximately proportional to the magnon specific heat, one may expect the variation of S with temperature as T 3/2 for ferromagnetic materials [22,32]. In view of these arguments, one may conclude that the observed peak may be attributed to the magnon drag effect.…”

“…The electrical resistivity measurements were also carried out using four-point probe method by collecting the data in heating mode over a temperature range 77-300 K. Finally, a dynamic two probe differen-0925-8388/$ -see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.03.067 tial method was employed for the measurement of thermopower [22]. The samples were coated with silver paint between two copper electrodes with adjustable temperature gradient and were monitored using copper-constantan thermocouples.…”