Synthesis, Structural Characterization, and Thermal Insulation Properties of SrLaM_0.5Al_0.5O₄ (M = Mn, Fe, Co) Ruddlesden-Popper Oxides

Ruddlesden-Popper (RP) oxide phases with the general formula A_n+1B_nO_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_0.5Al_0.5O₄, SrLaFe_0.5Al_0.5O₄, and SrLaCo_0.5Al_0.5O₄, 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 K₂NiF₄-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_0.5Al_0.5O₄ achieving the lowest value of 0.204 W/mK, followed by SrLaCo_0.5Al_0.5O₄ (0.326 W/mK) and SrLaFe_0.5Al_0.5O₄ (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_0.5Al_0.5O₄ as a promising low-thermal-conductivity oxide ceramic, with potential relevance to thermal barrier coating and high-temperature insulation applications.