[en] Mass-spectrometric method is used to study composition and to measure vapor component partial pressures above HfO₂-Sc₂O₃ system solid solutions with Sc₂O₃ content 10, 20 and 50%. Pressure-composition dependences for 2600 K are calculated. Positive deviation of ScO pressure dependence on Sc₂O₃ molar part in solid solution from linear one is evident. For HfO linear dependence within measurement error is fulfilled. Correlation between oxide relative volatility over the system and the value of interparticle interaction Me^Zx+-O^2x- is noticed