Crystal Structure of La₄Si₂O₇N₂ Analyzed by the Rietveld Method Using the Time-of-Flight Neutron Powder Diffraction Data

Abstract

The polycrystalline single-phase sample of La 4 Si 2 O 7 N 2 was prepared at 1773 and 1873 K by the gas-pressured sintering method. The structure refinement was carried out by the Rietveld method using time-of-flight neutron powder diffraction data measured at 297 K. La 4 Si 2 O 7 N 2 is isostructural with the Y 4 Al 2 O 9 high-temperature phase and crystallizes in a monoclinic cell, P2 1 /c (No. 14-1), Z ) 4. The lattice parameters refined for the sample prepared at 1773 K were a ) 8.0375( 2) Å, b ) 10.9900(2) Å, c ) 11.1115(2) Å, and β ) 110.9214(14)°. Nitrogen atoms statistically occupy the bridging site and the terminal sites of Si 2 O 5 N 2 ditetrahedra in the La 4 Si 2 O 7 N 2 structure. The nonmetal sites surrounded by La atoms only are fully occupied by oxygen atoms.

Synthesis and Luminescence Properties of Amber Emitting La7Sr[Si10N19O3] : Eu2+ and Syntheses of the Substitutional Variants RE8‐xAEx[Si10N20‐xO2+x] : Eu2+ with RE=La, Ce; AE=Ca, Sr, Ba; 0≤x≤2

“…Interatomic La−N/O distances are in the range of 2.41(2)–3.30(2) Å, while Sr/La−N distances vary from 2.62(2) to 3.37(2) Å and Si−N/O distances are between 1.65(1) to 1.77(1) Å and Si−N between 1.64(2) to 1.70(2) Å, which are in good agreement with reported values of other RE − AE −Si−N−O compounds [33–41] . For the substitutional variants RE 8‐ x AE x [Si 10 N 20‐ x O 2+ x ] : Eu 2+ ( RE =La, Ce; AE =Ca, Sr, Ba; 0≤ x ≤2), the mixed occupied sites La/Sr9‐12 can be substituted by Ce and Ca or Ba, respectively, whereas Ca 2+ could also occupy solely La 3+ occupied sites due to similar ionic radii.…”

Down-Conversion Nitride Materials for Solid State Lighting: Recent Advances and Perspectives

“…Lanthanide oxonitridosilicates are interesting hosts for Ce 3+ . − Blue emission is mostly seen in Ce 3+ -doped oxonitridosilicates, with exceptions in La 3 BaSi 5 N 9 O and Y 3 Si 5 N 9 O that emit orange colors. van Krevel et al reported the luminenscence of Ce 3+ in Y–Si–O–N compounds, including YSiO 2 N, Y 5 (SiO 4 ) 3 N, Y 2 Si 3 O 3 N 4 , and Y 4 Si 2 O 7 N 2 .…”

Preparation and luminescence properties of Ce3+ and Ce3+/Tb3+-activated Y4Si2O7N2 phosphors

“…Among several tricolor phosphors, rare-earth silicon-oxynitrides of Ln 4 Si 2 O 7 N 2 (Ln = Y, Lu, Gd, and La) [6][7][8][9][10] have been found and characterized. The structures of the silicon-oxynitrides typically consist of SiN 4 tetrahedra, and the partial nitrogen of the SiN 4 tetrahedra can be replaced by oxygen to form Si[ON] 4 tetrahedra.…”