Group II element nitrides M3N2 under pressure: a comparative density functional study

• Published in: Physica status solidi. B. Basic research Vol. 246; no. 7; pp. 1604 - 1613
• Main Authors: Römer, S. Rebecca, Dörfler, Thilo, Kroll, Peter, Schnick, Wolfgang
• Format: Journal Article
• Language: English
• Published: Berlin WILEY‐VCH Verlag 01-07-2009; Wiley-VCH
• Subjects: 61.50.Ah; 61.50.Ks; 64.60.Ej; 71.15.Mb; 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; High-pressure and shock-wave effects in solids and liquids; Mechanical and acoustical properties of condensed matter; Physics; Structure of solids and liquids; crystallography; Nitrides; Hexagonal lattices; Pressure effects; Ground states; II-VI semiconductors; Density functional method; High pressure; Polymorphism
• ISSN: 0370-1972; 1521-3951
• DOI: 10.1002/pssb.200945011

The high‐pressure behavior of group II element nitrides M3N2 (M=Be, Mg, Sr, and Ba) was studied up to 100 GPa and beyond. Evaluating a manifold of hypothetical polymorphs of composition A3X2 leads to proposing a new high‐pressure polymorph of Be3N2 with an anti‐A‐sesquioxide structure appearing at 82 GPa. Two high‐pressure phases were found for Mg3N2: first an anti‐B‐sesquioxide‐type structure should appear at 21 GPa followed by an anti‐A‐sesquioxide‐type structure at 65 GPa. While structure and true nature of Sr3N2 and Ba3N2 are not yet experimentally determined, we identified an anti‐bixbyite structure to be the ground state structure of Sr3N2 and a distortion variant of the anti‐A‐sesquioxide‐type structure as lowest energy modification for Ba3N2. For Sr3N2 the sequence of high‐pressure phases are (1) an anti‐Rh2O3‐II structure appearing at 3 GPa, (2) an anti‐B‐sesquioxide structure becoming most stable at 12 GPa and (3) a hexagonal P 63/mmc structure favored at 26 GPa. The development of the c /a ‐ratio of anti‐A‐sesquioxide Ba3N2 under pressure was examined, revealing a gradual reduction under pressure. Three high‐pressure polymorphs are then further proposed for Ba3N2: (1) an anti‐Rh2O3‐II structure at 2 GPa, (2) an anti‐CaIrO3 structure at 32 GPa and (3) a hexagonal P 63/mmc structure at 52 GPa. The results for all group II element nitrides M3N2 were compared. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)