From Minor Side Phases to Bulk Samples of Lanthanum Oxonitridosilicates: An Investigation with Microfocused Synchrotron Radiation

Abstract

Microcrystals of the oxonitridosilicate oxide La(11)Si(13)N(27.636)O(1.046):Ce(3+) were obtained by exploratory high-temperature synthesis starting from La, La(NH2)3, Si(NH)2, BaH2, and CeF3. Owing to the small size of the crystals, microfocused synchrotron radiation was used for structure investigations (space group Cmc21 (No. 36), a = 9.5074(4) Å, b = 32.0626(9) Å, c = 18.5076(8) Å, Z = 8, R1(all) = 0.0267). The crystal structure consists of an unprecedented interrupted three-dimensional network of vertex-sharing SiN(4-x)O(x) tetrahedra that form channels of siebener rings along [100]. Moreover, the structure is characterized by layers of condensed sechser rings in a boat conformation and vierer rings, which are alternatingly stacked with layers of vierer and dreier rings. Several split positions indicate two different local structure variants. Infrared spectroscopy confirms the absence of N-H bonds. Powder X-ray diffraction data show that bulk samples contain only a small amount of La(11)Si(13)N(27.636)O1.046:Ce(3+). However, once the exact composition was determined from structure analysis, it was possible to optimize the synthesis using fluorides as starting materials. Thereby, bulk samples of the homeotypic compound La(11)Si(13)N(27.376)O(0.936)F were obtained and investigated.

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.…”

“…Q 2 -type SiN [2] 2 (N 0.25 O 0.75 ) [1] 2 tetrahedra are only interconnect within one unit or equal units along [100] forming dreier rings in the (100) plane (Figure S5). Accordingly, the seeming achter ring channels as viewed along [100] are not closed achter rings [33][34][35][36][37][38][39][40][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. For charge compensation, this requires the simulta-neous incorporation of oxygen on the mixed occupied anionic sites, leading to SiN 2 (N 1/2-x/4 O 1/2 + x/4 ) 2 (0 � x � 2) tetrahedra.…”

Structure Elucidation of Complex Endotaxially Intergrown Lanthanum Barium Oxonitridosilicate Oxides by Combination of Microfocused Synchrotron Radiation and Transmission Electron Microscopy

“…According to various examples in literature and very low O contents suggested by EDX, initially a model with only SiN 4 tetrahedra was considered. [ 10 , 25 , 26 ] Discrete non‐tetrahedral anions were assigned as O in both cases according to Pauling's rule and as their distances of 2.26(2) Å to the nearest cations are in the range of La−O bonds but too short for La−N bonds. [ 27 , 28 , 29 ] Ba : La ratios for each position were then derived by BVS (Table S6) and transferred with minor corrections to achieve charge neutrality to the single‐crystal structure refinements as fixed values.…”

“…However, it is sometimes impossible to obtain sufficiently sized single crystals or phase pure powder samples from various syntheses, which often require extreme conditions, to elucidate the structure of new compounds with conventional single‐crystal or powder X‐ray diffraction. [10] Challenges concerning the structure determination of microcrystalline and often inhomogeneous samples have recently been approached by the combination of transmission electron microscopy (TEM) – especially selected area electron diffraction (SAED), scanning transmission electron microscopy (STEM) and energy dispersive X‐ray spectroscopy (EDX) – with synchrotron methods that exploit the brilliance of microfocused X‐ray beams. [ 11 , 12 ] Since the advent of compound refractive lenses,[ 13 , 14 , 15 , 16 ] synchrotron beams can be focused down to less than 1 μm, which enables the collection of single‐crystal X‐ray data from crystallites with the same size that have been pre‐characterized by TEM.…”

Zeolite-like Topology Oxonitridosilicate La3.6Ba1.7Si5N10O2.1 with Potential Applications in Nonlinear Optical Materials

“…Owing to the vast structural diversity and the variable properties of (oxo)­nitridosilicates, there has been sustained interest in exploring new (oxo)­nitridosilicates in chemistry and materials science. Over the past few years, Schnick et al have discovered a multitude of novel AB 2 -type tetrahedral network (oxo)­nitridosilicates and (oxo)­nitridophosphates. − These (oxy)­nitride compounds exhibit a diverse range of properties and unique structural features, such as ammonia adsorptions and storage in clathrate compound P 4 N 4 (NH) 4 (NH 3 ), and new zeolite topologies, for example, the NPO (nitridophosphate one) framework type Li x H 12– x – y + z [P 12 O y N 24– y ]­X with X = Cl, Br and Ba 19 P 36 O 6+ x N 66– x Cl 8+ x ( x ≈ 4.54) NPT (nitridophosphate two) framework type. The oxonitridosilicates Ba 3 Si 3 N 5 OCl and Ba 6 Si 6 N 10 O 2 (CN 2 ) are also under the category of NPO type. , Additionally, another significant application includes the phosphor host for Eu 2+ and Ce 3+ ions in the application of phosphor-converted light-emitting diodes (pc-LEDs) such as Ba 3 P 5 N 10 X:Eu 2+ (X = Cl, Br, I). , Furthermore, nitrides have exhibited promising properties and potential applications within the field of nonlinear optical (NLO) materials, for example, M 2 Si 5 N 8 with M = Ca, Sr, Ba, which exhibit high refractive indices and effective M eff ; these values were found to be comparable to those of the benchmark compound LiIO 3 . , The mixed-anion tetrahedra in oxonitridosilicates, e.g., (SiNO 3 ) 5– , (SiN 2 O 2 ) 6– , and (SiN 3 O) 7– , offer an alternative solution to address the limitations in birefringence of silicates.…”