High quality thin films of thermoelectric misfit cobalt oxides prepared by a chemical solution method

Abstract

Misfit cobaltates ([Bi/Ba/Sr/Ca/CoO]nRS[CoO2]q) constitute the most promising family of thermoelectric oxides for high temperature energy harvesting. However, their complex structure and chemical composition makes extremely challenging their deposition by high-vacuum physical techniques. Therefore, many of them have not been prepared as thin films until now. Here we report the synthesis of high-quality epitaxial thin films of the most representative members of this family of compounds by a water-based chemical solution deposition method. The films show an exceptional crystalline quality, with an electrical conductivity and thermopower comparable to single crystals. These properties are linked to the epitaxial matching of the rock-salt layers of the structure to the substrate, producing clean interfaces free of amorphous phases. This is an important step forward for the integration of these materials with complementary n-type thermoelectric oxides in multilayer nanostructures.

Thermoelectric and thermal transport properties of complex oxide thin films, heterostructures and superlattices

“…We will not focus our discussions on Ca 3 Co 4 O 9 , as this material has received considerable attention in a recent review article, 35 but we will discuss the growth efforts on Bi 2 Sr 2 Co 2 O y and related compounds. [141][142][143][144][145][146][147][148][149][150] The common techniques used for the growth of cobaltates were pulsed laser deposition, chemical solution deposition, and RF sputtering. Figure 6 documents some of the x-ray (h-2h scans and f-scans) and microscopic analyses performed on thin films of cobaltates.…”

Spontaneous cationic ordering in chemical-solution-grown La2CoMnO6 double perovskite thin films

“…As a chemical solution route, PAD provides an attractive opportunity to grow films close to thermodynamic equilibrium conditions. The characteristic growth conditions of PAD have already been shown to be advantageous for the stabilization of materials with complex structures or chemical composition, such as misfit cobalt oxides 29 and Y 3 Fe 5 O 12 yttrium iron garnet 30 . On the other hand, PAD might also be useful to clarify the role of structural strain in stimulating spontaneous cationic ordering because it has been shown that structural strain accommodation may proceed in a different way in samples prepared by PAD.…”

How does the spin-state of Co ions affect the insulator-metal transition in Bi2A2Co2O8 (A = Ca, Sr, Ba)?

“…Then the crystal energy is further optimized by reducing crystal symmetry. P-1 crystal group is finally obtained and its optimized lattice parameters are listed in Table 1 together with those of measured ones141529 listed in Table 2. The overall agreement is reasonable and discrepancy mainly results from the extra oxygens in the non-stoichiometric samples.…”