[摘要]：starting from the ambient-pressure phase Ca2Si5N8. HP-Ca2Si5N8 crystallizes in the orthorhombic crystal system (Pbca (no. 61), a = 1058.4(2), b = 965.2(2), c = 1366.3(3) pm, V = 1395.7(7) ?106 pm3, Z = 8, R1 = 0.1191). The HP-Ca2Si5N8 structure is built up by a three-dimensional, highly condensed nitridosilicate framework with N[2] as well as N[3] bridging. Corrugated layers of corner-sharing SiN4 tetrahedra are interconnected by further SiN4 units. The Ca2+ ions are situated between these layers with coordination nos. 6 + 1 and 7 + 1, resp. HP-Ca2Si5N8 as well as hypothetical orthorhombic o-Ca2Si5N8 (isostructural to the ambient-pressure modifications of Sr2Si5N8 and Ba2Si5N8) were studied as high-pressure phases of Ca2Si5N8 up to 100 GPa by using d. functional calcns. The transition pressure into HP-Ca2Si5N8 was calcd. to 1.7 GPa, whereas o-Ca2Si5N8 will not be adopted as a high-pressure phase. Two different decompn. pathways of Ca2Si5N8 (into Ca3N2 and Si3N4 or into CaSiN2 and Si3N4) and their pressure dependence were examd. It was found that a pressure-induced decompn. of Ca2Si5N8 into CaSiN2 and Si3N4 is preferred and that Ca2Si5N8 is no longer thermodynamically stable under pressures exceeding 15 GPa. Luminescence investigations (excitation at 365 nm) of HP-Ca2Si5N8:Eu2+ reveal a broadband emission peaking at 627 nm (FWHM = 97 nm), similar to the ambient-pressure phase Ca2Si5N8:Eu2+.
