Solid Solubility and Polymorphism in the System Sr₂SiO₄-Sr₂GeO₄-Ba₂GeO₄-Ba₂SiO₄

Abstract

Th2 reciprocal salt pair Sr,SiOl-Sr,GeO*-Ba,Ge04-Ba,SiOl was investigated using X-ray powder diffraction and DTA. Unlimited solubility in the lOW-&S04 structure type ( a ' ) occurs throughout the system above 85°C. The nonlinear changes of some lattice constants of the solid solutions are discussed. A stable monoclinic low-temperature ( p ) form of Sr,SiO, was found which converts reversibly to the high-temperature d-modification at 85'C. The enthalpy of the P-N' transition is 51 cal/mol. In the reciprocal salt pair the p-form solid solutions occur in a very narrow region below 85°C.

The β <-> α' phase transition of Sr2SiO4. II. X-ray and optical study, and ferroelasticity of the β form

“…A similar sharp change is observed in the cooling cycle. This discontinuous character of the phase transformation agrees with DSC data (Pieper et al, 1972), which would support a first-order thermodynamic classification. A peculiar behaviour is also shown by the c cell edge, which increases regularly with temperature both for the fl and for the a' phases, but decreases sharply and significantly in the fl --, a' passage.…”

“…According to optical and X-ray diffraction results, the fl = a' phase transition of Sr2SiO4 occurs sharply in both directions with a thermal hysteresis of 9-10 K. These properties, together with the enthalpy change of 210 J mol -x observed by Pieper et al (1972), would be evidence for the transformation being of first order. On the basis of structural data, the high-temperature form appears to be positionally (Sr atoms) and orientationally (SiO 4 groups) disordered (however, cf.…”

“…The transition between the low-fl and the high-a' forms is reported by Pieper, Eysel & Hahn (1972) to occur at about 358 K by DTA measurements, with a small but significant enthalpy change of 210 J mol -~ (DSC results). A large number of compounds in the A2BX4 family are isostructural with either a'-or fl-Sr2SiO 4, and some show both modifications and the corre-THE fl= a' PHASE TRANSITION OF Sr2SiO 4.…”

“…The fl structure is observed for Ba2TiO4 (Bland, 1961). Further, Ca2SiO4, Na2BeF4 and Eu2SiO4 are reported to crystallize in both forms (Pieper et al, 1972). The phase transition for Ca2SiO4, which occurs at about 973 K, was investigated by Saalfeld (1975) using X-ray oscillation photographs.…”

The enhancement of photoluminescence characteristics of Eu-doped barium strontium silicate phosphor particles by co-doping materials

“…Especially, the chromaticity of the (Ba,Sr) 2 SiO 4 :Eu phosphor particles could be controlled by changing the ratio of barium and strontium of the host material. (Ba,Sr) 2 SiO 4 :Eu phosphor particles were prepared and optimized by the conventional solid state reaction method [8][9][10][11][12][13]. In order to improve the photoluminescence characteristics of (Ba,Sr) 2 SiO 4 :Eu phosphor, several rareearth materials were employed as co-dopant in the solid state reaction method [14].…”