“…From a general point of view, the synthesis of HfSiO 4 was reported by high temperature solid state chemistry, 1,5,7,13,[21][22][23][24][25] sol-gel methods, 12,26,27 chemical transport reaction, 14,28,29 physical vapor deposition 30 and hydrothermal synthesis. 31,32 However, the only hydrothermal syntheses were reported by Caruba et al under acid conditions at T = 800°C, 75 MPa, 31 and by McNeil et al in very acid conditions, i.e.…”