Experimental Determinations of the High-Pressure Crystal Structures of Ca₃N₂

Abstract

Using synchrotron angle-dispersive X-ray diffraction and Raman spectroscopy techniques in a diamond anvil cell, we have examined the structural behaviors of the cubic (anti-C) Ca 3 N 2 at high pressures and room temperature. Two first-order phase transformations were observed at 9.6 and 19.5 GPa accompanied by large volume collapses of 7 and 9%, respectively. The two high pressure phases were identified as monoclinic (anti-B) and hexagonal (anti-A) structures by Rietveld refinement. With the pressure derivatives fixed at 4, the bulk modulus of anti-C, anti-B, and anti-A type structures were determined as 53.1(2), 61.6(4), and 83.9(2) GPa, respectively, indicating the increased incompressibility of Ca 3 N 2 under high pressure. The phase sequence observed in Ca 3 N 2 is in accordance with the systematic behavior of C f B f A phase transitions occurring in most sesquioxides.

Structural phase transition of ternary dielectric SmGdO3: Evidence from angle dispersive x-ray diffraction and Raman spectroscopic studies

“…The rare-earth sesquioxides RE 2 O 3 , (where RE = rare-earths) have attracted great deal of interest from a scientific and technological viewpoint. [1][2][3][4][5][6] Due to their various polymorphs and variety of applications, such as laser rods, phosphors, abrasive and refractory materials. The partial filling of the inner 4f electron shells, leading to well known lanthanide contraction, affects the physical properties of rare earth metals as well as rare earth sesquioxides.…”

“…[1][2][3][4][5][6] The partial filling of the inner 4f electron shells, leading to well known lanthanide contraction, affects the physical properties of rare earth metals as well as rare earth sesquioxides. [3][4][5][6] However, 4f electrons do not participate in bonding and behave like core electrons. The screening of the 4f electrons by the Xe core makes the bulk properties of lanthanides somewhat insensitive to addition of electrons in the 4f shell.…”

“…Furthermore, the exotic and rich physical properties of these oxides could be tuned by external pressure and temperature, which induce significant crystallographic and electronic changes. [5][6][7] Recently, some of the rare-earth sesquioxides (REOs) have attracted considerable attention as high-k dielectric materials in order to replace the conventional gate dielectric material, silicon dioxide, in complementary metal-oxide semiconductor (CMOS) technology. [8][9][10] Interestingly, some of REOs were found to possess variable dielectric constant depending on their crystal structure.…”

High-Pressure Synthesis of the β-Zn3N2 Nitride and the α-ZnN4 and β-ZnN4 Polynitrogen Compounds

“…Five binary nitrides, Be 3 N 2 , Mg 3 N 2 , Ca 3 N 2 , α-Zn 3 N 2 , and Cd 3 N 2 , are known to adopt the anti-bixbyite structurean anti-structure of the well-known type-C (i.e., anti-C) rare earth sesquioxides (Sc 2 O 3 , Y 2 O 3 , Er 2 O 3 , Gd 2 O 3 , In 2 O 3 )stable at ambient conditions. Under pressure, Mg 3 N 2 and Ca 3 N 2 both follow the typical sequence of pressure-driven phase transitions for rare earth sesquioxides, namely, from anti-C ( Ia 3̅) → anti-B ( C 2/ m ) → anti-A ( P 3̅ m 1). The synthesis of β-Zn 3 N 2 with the anti-Rh 2 O 3 structure type at 35.0 GPa suggests that α-Zn 3 N 2 undergoes an alternative transformation route under pressure: from anti-C ( Ia 3̅) to an anti-Rh 2 O 3 structure.…”

Ca3N2 and Mg3N2: Unpredicted High-Pressure Behavior of Binary Nitrides

“…The selected models base on the HP-behavior of corundum. Concerning the highpressure behavior of M 3 N 2 (M = Ca, Mg), there are experimental and theoretical investigations of Hao et al, 29,30 of which the theoretical results are in agreement with the ones of R€ omer et al 27,28 However, the proposed high-pressure phases are not supported by the experimental XRD patterns displayed in refs 29 and 30. The appearance of two new weak reflections is most probable due to reactions of M 3 N 2 (M = Ca, Mg) with the used but inappropriate pressure medium silicone oil.…”