MgSiN2

Contents

• Crystal Structures

• Synthesis and Growth Methods

• Electronic Band Structure

• Vibrational Properties

• Elastic Properties

Crystal Structures

Space group: Pna2₁ (or Pbn2₁ with current axes choice).

(NOTE: For the crystal modeling purposes, select the spacegroup as Pbn2₁ )

Point group: C_2v

Lattice constants:

Wyckoff positions:

GGA [2]

LP phase, LDA [4]

LP phase, PBE [4]

LP phase, experimental [5]

LP-phase means the usual Pbn2₁ phase.

Phase transitions under pressure.

A phase transition to a trigonal phase with space group R-3m (No. 166) is predicted in [3]

to occur at 17.45 GPa (GGA-PBEsol), 19.05 (LDA-CAPZ), 25.0 GPa (GGA-PW91) depending on which

exchange correlation is used. For further detail on this structure in which Si is octahedrally coordinated

and occuring in layers with Mg ions in between, see [3].

Synthesis and Growth Methods

1. By mixing Mg metal (Alfa Aesar, 99.98%) and silicon diimide in an Argon atmosphere with heating the system to 1650^o C. [7]

2. MgSiN₂ powders were synthesized by heating Mg and Si₃N₄ powders in a horizontal tube furnace for 16 hours at 1000^o C under a flowing N₂ atmosphere in a Mo boat, followed by cooling at a rate of 5^o C/min. under the same N₂ flow. [6]

3. MgSiN₂ synthesis using an axially symmetric vertical reactor with a graphite reactor unit. [8]

Electronic band structure

Band gap:

Figures:

Figure 1: QSGW electronic band structure of MgSiN₂ [2]

Figure 2: Electronic band structure of MgSiN₂ obtained using the HSE approximation. Reproduced from [6], with the permission of AIP Publishing.

Figure 3: Electronic band structure of MgSiN₂ obtained using GGA. Reproduced from [7], with the permission of AIP Publishing.

Figure 4: Fine structure of the bands near the valence band maximum with symmetry labeling for MgSiN₂ [2]

Figure 5: Total and partial densities of states of MgSiN₂ [2]

More information available for electronic structure (high and low Pressure) in [4]

Vibrational Properties

There are 12 modes of each a₁, a₂, b₁, and b₂ symmetry.

All modes are Raman active. The a₁, b₁, b₂ are IR active as well. Longitudinal modes a_1L, b_1L, b_2L are affected by LO-TO splitting.

Phonon frequencies (in cm^-1):

Reference: [9]

Predicted Raman and IR spectra can be found in ref. [9] as well as phonon band structure and density of states.

Calculated phonon frequencies were also reported in [10] but only in figure format.

Raman spectra measured on a powder were reporte in [10] and are reproduced below.

From [10].

Born effective charge tensor components: