文摘
Theoretical and experimental methods have been conducted to study the high-pressure structures of CaWO4, which have never been definitely determined during the past decades. By using the CALYPSO method, in addition to the previously known tetragonal scheelite structure (I41/a), monoclinic fergusonite structure (I2/a), and the orthorhombic structure (Cmca) predicted by previous works, we have found two other new phases of CaWO4 at higher pressure: monoclinic P21/c and P21/m structures. Although the P21/c structure has the lowest energy (above 26.0 GPa), synchrotron-radiation-based X-ray diffraction measurements show that only the P21/m structure stably exists above 38.0 GPa. The kinetical hindrance of P21/c structure formation in the experiment has been attributed to its larger W-O coordination number than that of the P21/m structure at high pressure.