Na₈CeSi₆O₁₈ and Its Ti-Doped Analogue Na₈Ce_0.73Ti_0.27Si₆O₁₈ with Interesting Photovoltaic Properties

Na₈CeSi₆O₁₈ and Na₈Ce_0.73Ti_0.27Si₆O₁₈ (denoted CeSiO-CJ11A and CeTiSiO-CJ11B, respectively) were the first successful examples of Ce⁴⁺ and Ce⁴⁺/Ti⁴⁺ mixed silicates synthesized under mild hydrothermal conditions at 503 K. Their isostructure is confirmed by the powder X-ray diffraction (XRD) analysis. The single-crystal XRD analysis of CeSiO-CJ11A reveals that its structure is comprised of [Si₆O₁₈]_n^12n– cyclosilicate anions that are linked via CeO₆ octahedra, giving rise to a three-dimensional (3D) framework that contains 6-membered ring channels delimited by the SiO₄ tetrahedra and CeO₆ octahedra along the [101]-direction. Charge neutrality is achieved by Na⁺ ions located in the channels. Interestingly, the surface photovoltage (SPV) and transient photovoltage (TPV) studies of CeSiTiO-CJ11B show that it exhibits n-type semiconductor characteristics and a slow recombination process.