High-pressure phases and transitions of the layered alkaline earth nitridosilicates SrSiN₂and BaSiN₂

Abstract

We investigate the high-pressure phase diagram of SrSiN 2 and BaSiN 2 with density-functional calculation. Searching a manifold of possible candidate structures, we propose new structural modifications of SrSiN 2 and BaSiN 2 attainable in high-pressure experiments. The monoclinic ground state of SrSiN 2 transforms at 3 GPa into an orthorhombic BaSiN 2 type. At 14 GPa a CaSiN 2 -type structure becomes the most stable configuration of SrSiN 2 . A hitherto unknown Pbcm modification is adopted at 85 GPa and, finally, at 131 GPa a LiFeO 2 -type structure. The higher homologue BaSiN 2 transforms to a CaSiN 2 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.

Nitridosilicates and Oxonitridosilicates: From Ceramic Materials to Structural and Functional Diversity

“…[25] several hitherto unknown high-pressure polymorphs of MSiN 2 with M = Be, Mg, Ca. [84] The quaternary lithium alkaline earth nitridosilicates Li 2 MSi 2 N 4 with M = Ca, Sr form an established network structure. [85] In this case, the structure is closely related to that of BaAl 2 S 4 , BaGa 2 S 4 , and the high-pressure modifications of the borates MB 2 O 4 (M = Ca, Sr), which are reported to crystallize in Net 39. , they are used industrially in pc-LEDs as highly efficient red-to-orange emitting luminescent materials (see Section 7.5).…”

Nitridosilicate und Oxonitridosilicate: von keramischen Materialien zu struktureller und funktioneller Diversität

“…[25] Zudem wurden hochkondensierte, dreidimensionale Hochdruckmodifikationen von SrSiN 2 und BaSiN 2 anhand von Dichtefunktionalrechnungen vorhergesagt. [59] Das Oxonitridosilicat CaSi 2 O 2 N 2 hat eine unerwartete Struktur. Gemäß der empirischen Formel und dem entsprechenden Kondensationsgrad von k = 1 = 2 würde man eine dreidimensionale Gerüststruktur aus eckenverknüpften [SiX 4 ]-Tetraedern (X = O, N) erwarten.…”

HP‐CaSiN2 – A New High‐Pressure Modification

“…The search for compounds with similar compositions and structures in the data base gave no consistence and a trial of indexing with the program STOE WinXPOW [48] was not successful. As well the crystal structures of the predicted HP-phases of Römer et al [38][39][40] did not match with the observed reflections of the new phase.…”

“…DFT‐calculation by Römer et al concerning novel high‐pressure phases of the MSiN 2 ‐compounds (M = Ca, Sr, Ba) predicted two new HP‐modifications for CaSiN 2 (β‐CaSiN 2 at 1.6 GPa with CaGeN 2 ‐structure type and γ‐CaSiN 2 at 60 GPa with LiFeO 2 ‐structure type), which has led to intense investigations of the HP‐behavior of the MSiN 2 ‐compounds (M = Mg, Ca, Sr, Ba) . In this contribution the new form HP‐ CaSiN 2 is reported.…”

“…Additionally, CaSiN 2 :Ce 3+ is proposed to be one of few phosphors that can be excited in the yellow-green region, where chlorophyll is ineffective and down-converts the light into red photons, what could be used in plant-growth enhancement. [24] DFT-calculation by Römer et al [38][39][40] concerning novel highpressure phases of the MSiN 2 -compounds (M = Ca, Sr, Ba) predicted two new HP-modifications for CaSiN 2 ( -CaSiN 2 at 1.6 GPa with CaGeN 2 -structure type [41] and γ-CaSiN 2 at 60 GPa with LiFeO 2 -structure type), which has led to intense investigations of the HP-behavior of the MSiN 2 -compounds (M = Mg, Ca, Sr, Ba). [42] In this contribution the new form HP-CaSiN 2 is reported.…”