Corrigendum: Sol-gel Synthesis of TiO2 With p-Type Response to Hydrogen Gas at Elevated Temperature - Xie, Lijuan; Li, Zhong; Sun, Linchao; Dong, Baoxia; Fatima, Qawareer; Wang, Zhe; Yao, Zhengjun; Haidry, Azhar Ali (Frontiers in Materials, 2019)