Synthesis, Structural Characterization, and Thermal Insulation Properties of SrLaM 0.5 Al 0.5 O 4 (M = Mn, Fe, Co) Ruddlesden-Popper Oxides

Abstract

Ruddlesden-Popper (RP) oxide phases with the general formula A n+1 B n O 3n+1 have attracted significant interest as thermally insulating ceramics owing to their intrinsic layered crystal architecture, which promotes strong phonon scattering. In the present work, three novel n = 1 Ruddlesden-Popper oxides, SrLaMn 0.5 Al 0.5 O 4 , SrLaFe 0.5 Al 0.5 O 4 , and SrLaCo 0.5 Al 0.5 O 4 , were successfully synthesized by a conventional solid-state reaction route. Phase purity and crystal structure were confirmed by X-ray diffraction (XRD) analysis, which revealed a tetragonal K 2 NiF 4 -type structure (space group I4/mmm) consistent with previously reported RP phases. Surface morphology and grain characteristics were examined by scanning electron microscopy (SEM). Thermal conductivity measurements demonstrate that all three compositions exhibit notably low thermal conductivity, with SrLaMn 0.5 Al 0.5 O 4 achieving the lowest value of 0.204 W/mK, followed by SrLaCo 0.5 Al 0.5 O 4 (0.326 W/mK) and SrLaFe 0.5 Al 0.5 O 4 (0.496 W/mK). The superior thermal insulation performance of the Mn-containing compound is attributed to enhanced mass-contrast disorder at the B-site arising from the larger atomic-mass difference between Mn and Al, together with stronger phonon-phonon Umklapp scattering and increased grain-boundary density observed in SEM. These results establish SrLaMn 0.5 Al 0.5 O 4 as a promising low-thermal-conductivity oxide ceramic, with potential relevance to thermal barrier coating and high-temperature insulation applications.