Ce₂[CrN₃]: Single Phase Synthesis and Characterization of a Nitridochromate(I)

Abstract

The ternary nitridochromate Ce 2 [CrN 3 ] (orthorhombic Immm, a = 378.56(1) pm, b = 340.88(2) pm, c = 1251.27(4) pm) was synthesized in single phase form from the binary nitrides utilizing the decomposition of CrN to Cr 2 N. Magnetic susceptibility measurements * Prof. Dr. R. Niewa

On the Formation Mechanism of Chromium Nitrides: An in situ Study

“…At 1080°C a complete conversion of γ-CrN into β-Cr 2 N was observed in full agreement with literature. [28,29,36] In Rietveld refinements no significant deviation from ideal 1:1 composition of γ-CrN was found, while for β-Cr 2 N at 800°C an initial composition of β-Cr 2 N 0.95(7) was determined. With increasing phase fraction of β-Cr 2 N a more precise determination of its composition was possible: At 1080°C a composition of β-Cr 2 N 0.95(2) was observed in agreement to literature composition values [27] (see Table S1, Supporting Information).…”

“…[29] A lower reaction temperature of 445°C is possible resulting in markedly enlarged full width at half maximum (FHWM) of the reflections in X-ray diffraction. A complete conversion of chromium(III) chloride is achieved within 6 h. An increase in reaction temperature leads to reflections with smaller FHWM and coincidently, the oxygen impurity content of γ-CrN decreases from www.zaac.wiley-vch.…”

“…[30] Additionally, γ-CrN formation was reported in autoclave synthesis of γ-CrN above 400°C from chromium(III) chloride, ammonium chloride, and sodium as halide catcher. [40] Particularly, the ammonolysis of chromium(III) compounds like CrCl 3 [28,29] or Cr 2 S 3 [41] in flowing ammonia are interesting for γ-CrN production, due to lower reaction temperatures and better phase purities of the obtained products. However, for a successful production of high-purity β-Cr 2 N and γ-CrN via ammonolysis reactions, information on the formation mechanisms and thus potential intermediate phases determining e.g.…”

“…Chemical analysis of the respective samples showed a strong dependency of the N-poor phase boundary on the temperature (β-Cr 2 N 0.83 at 950°C and β-Cr 2 N 0.645 at 1350°C), whereas for the N-rich phase boundary only a small deviation was observed (β-Cr 2 N 0.979 at 950°C and β-Cr 2 N 0.974 at 1350°C). [27] β-Cr 2 N can be synthesized in single phase either via thermal decomposition of γ-CrN above 1050°C [28,29] or in solid state metathesis reactions of chromium(II) chloride, chromium(III) chloride, or chromium(III) oxide with lithium nitride Li 3 N, magnesium nitride Mg 3 N 2 , or calcium nitride Ca 3 N 2 at elevated temperatures. [30] γ-CrN crystallizes in the rock salt structure type [21] and the formation enthalpy was determined to -123 kJ·mol -1 , [31] thus γ-CrN is thermodynamically less stable than β-Cr 2 N. [27] For bulk samples of γ-CrN only very small deviations from the ideal 1:1 composition occur, [32,33] whereas for thin films vacancies in the chromium substructure in the sense of γ-Cr 1-x N were observed.…”

“…Chemical analysis of the respective samples showed a strong dependency of the N‐poor phase boundary on the temperature (β‐Cr 2 N 0.83 at 950 °C and β‐Cr 2 N 0.645 at 1350 °C), whereas for the N‐rich phase boundary only a small deviation was observed (β‐Cr 2 N 0.979 at 950 °C and β‐Cr 2 N 0.974 at 1350 °C) 27. β‐Cr 2 N can be synthesized in single phase either via thermal decomposition of γ‐CrN above 1050 °C28,29 or in solid state metathesis reactions of chromium(II) chloride, chromium(III) chloride, or chromium(III) oxide with lithium nitride Li 3 N, magnesium nitride Mg 3 N 2 , or calcium nitride Ca 3 N 2 at elevated temperatures 30…”