Influence of substrate temperature on the structural, morphological, and piezocatalytic performance of Ba2TiO4 films deposited by magnetron sputtering

Thin films of Ba_xTiO₄ (1.59 ≤ x ≤ 1.83) were fabricated via magnetron sputtering, and the influence of substrate temperature (T_s: 400–800 °C) on their structural, compositional, optical, and piezocatalytic properties was systematically investigated by various techniques including XRD, XPS, AFM, EDS, SEM, UV–vis DRS and PL. XRD analysis confirmed that films grown at 400 °C exhibit an amorphous phase, whereas well-crystallized Ba₂TiO₄ films with a monoclinic β phase are obtained at T_s above 550 °C. As T_s rises from 400 °C to 800 °C, there is a decrease in E_g from 3.84 eV to 3.58 eV. The piezocatalytic performance of the films was evaluated using methylene blue (MB) dye degradation as an indicator. The rate constant k is estimated to be in the range of 0.060–0.045 min⁻¹ for well-crystallized films grown at T_s values ranging from 700 to 800 °C, which is 5 to 3.75 times higher than that of amorphous films grown at 400 °C (k∼0.012 min⁻¹). The results show that by altering the substrate temperature during reactive sputtering, it is feasible to grow Ba₂TiO₄ thin films with some advantageous properties such as a higher Ba/Ti ratio, good crystallinity, low defect states and narrowed band gap, offering promising applications for piezocatalyzed degradation of organic pollutants in wastewater treatment.