Celsian ceramics based on hexagonal BaAl 2 Si 2 O 8 have been prepared through synthesis at 1450°C followed by firing at 1500°C. The unit cell parameters of BaAl 2 Si 2 O 8 and principal bond distances in its structure have been determined by the Rietveld method. Using differential thermal analysis and tempera ture dependent dielectric measurements, we have determined the temperature of the α (hexagonal) to β (hexagonal) phase transition in our samples: 280-320°C.

Crystal structure formation of BaAl2Si2O8 known as polymorphic compound is investigated in present work depending on conditions of preparation. Characteristics of ceramics have been studied for dierent modications of crystal structure. Additional technologic operations (grinding with following heat treatment) have been found to result in polymorphic transformation. Dielectric properties of BaAl2Si2O8 ceramics have been studied for hexagonal, monoclinic crystal structure modications as well as for that based on phase mixture. It has been shown that the sintering of ceramic material based on the monoclinic crystal structure modication of BaAl2Si2O8 takes place in temperature diapason of 13001350• C. Sintering of material with the hexagonal crystal structure modication occurs in temperature diapason of 14501500• C. Ceramics materials based on compound BaAl2Si2O8 are found to have low porosity, high Q-factor and dielectric characteristics, allowing use of these ceramic materials for production of resonators and other microwave equipments.

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