The origin of the change in type of the majority carrier in

Abstract

Electrical transport properties of polycrystalline ceramic specimens of the system (x = 0.05, 0.10, and 0.15) have been investigated as functions of temperature by means of complex-plane impedance analysis, dielectric properties, four-probe dc conductivity, Seebeck coefficients, and magnetic susceptibilities. The type of the majority carrier changes from electrons to holes when x increases from 0.10 to 0.15, because the Seebeck coefficient changes from negative to positive with x increasing from 0.10 to 0.15. The complex-plane impedance analysis distinguishes the bulk conduction from the conduction across grain boundaries. In a specimen with x = 0.15, the activation energy in the bulk conduction is nearly equal to that for the dielectric relaxation. This implies that the hopping process of small polarons of holes dominates the transport properties in this specimen above 190 K. The temperature dependencies of the magnetic susceptibilities indicate that the number of high-spin ions (S = 2) decreases with increasing x. The expansion of the lattice parameters and the increment of the ratio with increasing x suggest that ions are preferentially substituted for low-spin , which relaxes the rhombohedral structural distortion in the system. The change in the type of the charge carrier has been discussed in terms of the electronic structures deduced from these experimental results.

Characterization of La0.5Sr0.5Co0.5Ti0.5O3−δ as symmetrical electrode material for intermediate-temperature solid-oxide fuel cells

“…When Co(III) ions are substituted by Ti(IV), as reported in the LaCo 1Àx Ti x O 3 solid solution [20], a mixed valence system is obtained as the charge neutrality requires the partial reduction to divalent Co ions. Earlier studies of this system by Nakatsugawa and Bahadur [21,22] in the 0.05 x 0.15 composition ranges confirm this result.…”

Electric conduction and dielectric relaxation processes in solid oxide fuel cell electrolyte La0.5Sr0.5Ga0.6Ti0.4O3−δ

“…[14][15][16][17]22 Since the reciprocal resistance is proportional to the conductivity, temperature dependencies of the conductivities in the bulk and boundary, including activation energies, are to be estimated from Arrhenius relations of ln͑T / R b ͒ or ln͑T / R gb ͒ against 1 / T in Fig. 4.…”

“…Alternate current measurements (capacitances and impedances) have been carried out in the same way as the previous reports [14][15][16] using an Agilent 4294 A precision impedance analyzer with a frequency range of 40 Hz-10 MHz. The elctrodes for ac measurements have been made by coating Pt paste on both the largest surfaces of the specimen and by baking it at 900°C for 0.5 h. The details of dc measurements by the four-probe method are described elsewhere.…”

Phase formation, crystal structures and magnetic properties of perovskite-type phases in the system La2Co1+z(MgxTi1−x)1−zO6

“…An alternative way to change the properties of LaCoO 3 and similar compounds is to substitute Co in the B position by another ion of different charge and thus change the formal valence of Co. Several studies have been carried out in the system LaCo 1-x Ti x O 3 , where Ti 4+ is substituted for Co 3+ [11,33,34]. A solid solution is found to exist up to x = 0.5 [34].…”