Structure, microstructure, and high-temperature transport properties of La1−xCaxMnO3−δ thin films and polycrystalline bulk materials

Abstract

Single-phase samples of La1−xCaxMnO3−δ (LCMO), x≈0.3, prepared by pulsed reactive crossed beam laser ablation on SrTiO3 (STO) substrates, and soft chemistry synthesized powders were studied by various methods. The precise study of the crystal structure and microstructures by a combination of electron diffraction and high-resolution electron microscopy revealed a monoclinic distortion of the GdFeO3-type structure, P21/c space group, in both types of materials, i.e., the thin films and powder compound. The analysis of the LCMO/STO interface showed nonhomogeneous stress states and a composition that results in a different superstructure from the usual detected structure. The temperature-dependent thermoelectric power in the case of thin films presented an anomalous behavior compared to those from the powder compound. A structural transition at high temperature (T≈750 K) influences the thermopower behavior as well as the thermal conductivity values.

High-temperature thermoelectric properties of W-substituted CaMnO3

“…The twin domains likely occur because the CaMnO 3 compound undergoes a structural transition from a higher symmetry, cubic structure (the hightemperature structure), to a lower symmetry, orthorhombic structure (the low-temperature structure). Since the deviations from the cubic symmetry are small and the orthorhombic structure of CaMnO3 can be described with 2a x 2a x 2a unit cell, domains with different unit-cell orientations can grow coherently, thus yielding the observed twinning phenomenon 8,9 .…”

Thermoelectric oxide modules tested in a solar cavity-receiver

“…8 A series of four-leg TOMs were assembled by connecting the p-and n-type TE legs electrically in series and thermally in parallel between two electrically insulated and thermally conductive Al 2 O 3 plates (Rubalit 708 S, CeramTec GmbH, Plochingen, Germany) with a crosssection of 25 Â 25 mm 2 and a thickness of 0.5 mm. 18 The assembly drawing is shown in Fig.…”

“…[1][2][3][4] Oxide materials, especially with perovskitetype structure, can be easily synthesized with controllable composition and TE properties. [5][6][7][8] The low costs of these materials are beneficial as well. The advantage of Bi 2 Te 3 -based TE materials is the better performance 9,10 expressed by the figure-of-merit, ZT 5 S 2 T/qj, where S is the Seebeck coefficient, q is the electrical resistivity, and j is the thermal conductivity.…”

Thermoelectric Oxide Modules (TOMs) for the Direct Conversion of Simulated Solar Radiation into Electrical Energy

“…The thermal conductivity was evaluated indirectly by separate measurements of the thermal diffusivity (Netzsch LFA apparatus) and the specific heat (Netzsch DSC apparatus). The electric and thermal transport properties were measured in the temperature range of 300 K < T < 800 K. A detailed description of the TE measurements is reported in [ 18 ].…”