The solid solution crystals, La1–xNdxGaO3 and La1–xPrxGaO3 have been studied by differential scanning calorimetry method; the crystals exhibit the first order phase transition, the
temperature of the transition linearly increases with the concentration of Pr or Nd. The structure of the crystals has been
determined by X-ray diffraction. The correlation between the phase transition temperature and crystalline structure at the
temperature of the phase transition in both solid solution families is discussed.