Old and New Insights into Structure and Properties of Eu2[SiO4

Abstract

Lemon-yellow single crystals of Eu2[SiO4] were obtained by reaction of elemental europium with Eu2O3 in the presence of SiO2 carried out in evacuated silica ampules at 1373 K for 48 h followed by constant cooling to room temperature with 120 K per hour. Eu2[SiO4] crystallizes at room temperature in the larnite-type structure of β-Ca2[SiO4] (monoclinic, P21/n) with parameters a = 565.02(5), b = 709.15(6), c = 975.84(8) pm, β = 92.614(3)° for Z = 4. At 452 K it undergoes a reversible phase transition to an incommensurate structure similar to the isotypic compounds Sr2[SiO4] and K2[SeO4]. The phase transition energy was determined to 0.54(2) J·g–1 by DSC measurements and temperature dependent birefringence measurements show that the phase transition exhibits a significant hysteresis. Refinements of the structure of Eu2[SiO4] based on single crystal X-ray diffraction data show that the high temperature modification crystallizes in the orthorhombic space group Pnma(α00)0ss with a = 710.16(6), b = 566.93(5), c ...