Abstract: Physio-chemical reactions in emissive materials of the barium scandate dispenser cathode during the sintering process are investigated by X ray analysis with the aid of an X-ray diffractometer using CuK radiation. The emissive materials of barium scandate are the compounds resulting from the reaction and sintering of BaO-CaO-Al2O3-Sc2O3 with a specified proportion. During the course of the investigation, it became clear that the formation of different compounds is very dependent on the firing temperature.The results of experiments indicate that the phases present at 1000--1600℃ are the compounds of Ba-Al-O system, Ba-Sc-O system and CaO; at 1300--1500℃ a solid solution of Ba-al-Sc-O system is found, which is formed from Ba-Al-O and Ba-Sc-O system by their mutual solubility and belongs to a quasistable state of thermodynamics. the solid solution is first formed to be an orthorhombic unit cell for about 5BaO-Al2O3-Sc2O3 with a=9.725(2), b=8.698(3), c=6.152(3), and finally a tetragonal unit cell for about 4BaO-Al2O3-0.5Sc2O3 with a=14.4996(19), c=5.0265(8), and CaO is in the form of free state.