Layered atomic structures of double oxides for low shear strength at high temperatures

Double oxide phases combining a transition metal and a noble metal have recently become a subject of investigation as solid lubricant materials for high-temperature tribological applications. Here, we study the changes in chemistry and crystal structure of silver molybdate (Ag2Mo2O7) and silver tungstate (Ag2WO4) thin films and powders from 25 to 600 °C. We show, using ab initio molecular dynamics, high-temperature X-ray diffraction, high-temperature Raman spectroscopy and differential scanning calorimetry in combination with sliding tests, that the layered atomic structure of silver molybdate facilitates sliding, resulting in a low coefficient of friction (<0.2) from 300 to 500 °C.