High-pressure phases and transitions of the layered alkaline earth nitridosilicates SrSiN2 and BaSiN2

• Published in: Journal of physics. Condensed matter Vol. 21; no. 27; pp. 275408 - 275408 (5)
• Main Authors: Römer, S Rebecca, Kroll, Peter, Schnick, Wolfgang
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 08.07.2009; Institute of Physics
• Subjects: Condensed matter: structure, mechanical and thermal properties; Crystalline state (including molecular motions in solids); Crystallographic aspects of phase transformations; pressure effects; Exact sciences and technology; Physics; Structure of solids and liquids; crystallography; Nitrides; Phase diagrams; Inorganic compounds; Phase transformations; Displacive transformations; Density functional method; Structure modification; High pressure; Crystal structure
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/0953-8984/21/27/275408

We investigate the high-pressure phase diagram of SrSiN2 and BaSiN2 with density-functional calculation. Searching a manifold of possible candidate structures, we propose new structural modifications of SrSiN2 and BaSiN2 attainable in high-pressure experiments. The monoclinic ground state of SrSiN2 transforms at 3 GPa into an orthorhombic BaSiN2 type. At 14 GPa a CaSiN2-type structure becomes the most stable configuration of SrSiN2. A hitherto unknown Pbcm modification is adopted at 85 GPa and, finally, at 131 GPa a LiFeO2-type structure. The higher homologue BaSiN2 transforms to a CaSiN2 type at 41 GPa and further to a Pbcm modification at 105 GPa. Both systems follow the pressure-coordination rule: the coordination environment of Si increases from tetrahedral through trigonal bipyramidal to octahedral. Some high-pressure phases are related in structure through simple group-subgroup mechanisms, indicating displacive phase transformations with low activation barriers.