High-temperature electrical transport behaviors of the layered Ca2Co2O5-based ceramics

Abstract

Textured Bi-substituted Ca2Co2O5 ceramics have been prepared using a coprecipitation method combined with spark plasma sintering. The Bi substitution is effective in increasing the grain orientation of the Ca2Co2O5-based ceramics (from 0.46 to 0.85). Electrical conductivity increases obviously with partial substitution of Bi3+ for Ca2+ (from 113.9 to 142.4 S/cm at 973 K). The Ca1.92Bi0.08Co2O5 sample exhibits higher power factor (4.4×10−4 W m−1 K−2) than that of pure Ca2Co2O5 (3.2×10−4 W m−1 K−2) at 973 K, indicating that the Ca2Co2O5 system is another promising p-type material for high-temperature thermoelectric applications.

Tunning of microstructure and thermoelectric properties of Ca3Co4O9 ceramics by high-magnetic-field sintering

“…From the calculation result, j ch in the present samples is about 10% of the total thermal conductivity j, which is also shown in Table I. 20 The calculated phonon thermal conductivity from both the formula j ph ¼ j À j ch and j ph ¼ D  C p  d are almost the same; the phonon component j ph reaches 90% of the total thermal conductivity j for all samples. In the latter formula j ph ¼ D  C p  d, d is the density of the specimen, D is the thermal diffusivity, and C p is the specific heat of the samples.…”

“…20 As shown in Fig. 11, the linear relationship of ln q ab (T) versus T À1/3 indicates that the transport mechanism for all studied samples has turned into 2D-VRH in the lower temperature range.…”

“…10 If the variation takes place in CoO 2 layers, it not only produces strong disorder and distortion in the sample but also changes the transport mechanism, because the conduction path in the CoO 2 layer is disturbed. 20 In the low-temperature range, the hole hopping tends toward farther low-energy sites rather than neighbor sites, and consequently the VRH mechanism dominates the transport behavior in the present samples. Moreover, due to the anisotropic layered structure, the VRH transport is twodimensional.…”

“…As the temperature increases, the holes have high enough energy, and the transport mechanism changes from VRH to the thermal activated model. 20 That is why the plot of lnq ab (T) versus T À1/3 in Ca 3 Co 4 O 9 samples stays linear well in the low-temperature region below $25 K, but the linear relationship of lnq ab (T) versus T À1 gradually dominates in the high-temperature region above $25 K. With increasing sample sintering field, the activation energy E 0 decreases and the localization of carriers weakens gradually, so the thermal activated transport shifts to the lower temperature range.…”

Understanding the electronic and phonon transport properties of a thermoelectric material BiCuSeO: a first-principles study

“…Over the past five years, the ZT value of BiCuSeO has been continuously increased from 0.76 to 1.5 by doping to enhance the power factor as well as nanostructuring to further reduce the lattice thermal conductivity. Many experimental works on the transport properties of BiCuSeO indicate that the compound exhibit (1) a relatively larger Seebeck coefficient at optimized concentration (230 V / K  @873K [9], 243 V / K  @923K [10 ]), (2) [13]. Moreover, the low lattice thermal conductivity may originate from the interface phonon scattering and low-phonon-conductive heavy elements [4].…”