Ternary compounds of hydrogen, oxygen and sulfur at high pressures

The discovery of superconductivity in H₃S with the highest T_c of about 200 K at 200 GPa has motivated extensive recent studies of various binary hydride compounds with the goal of achieving a higher T_c at lower pressures. However, the current studies of binary hydride compounds have not shown much promise. Therefore, there is an interesting scientific question whether three-element ternary compounds would improve upon binary systems including H₃S. In this work, we examine a ternary system of hydrogen, sulfur and oxygen. The latter two elements are in the same group in periodic table, which might provide similar chemical bonding as well as improved superconducting properties. To test this hypothesis, we perform variable-composition first-principles evolutionary crystal structure search of H_xS_yO_z ternary compounds at high pressure. Phase diagrams of the ternary system are constructed. The chemical bonding in the predicted ternary compounds is analyzed and its effect on resulting electronic and vibrational properties is discussed in connection to the possibility of finding superconductivity on this ternary system.