Über hexagonale Perowskite mit Kationenfehlstellen. XXXIII. Verbindungen vom Typ Ba6−xSrxB2−y3+SEy3+W3□O18

On Hexagonal Perovskites with Cationic Vacancies. XXXIII. Compounds of Type Ba_6?xSr_xB_2?y³⁺SE_y³⁺W₃□O₁₈ In the series Ba_6?xSr_xLu_2?ySE_y³⁺W₃□O₁₈ a substitution of Sr²⁺ for Ba²⁺ is possible. According to intensity calculations on powder data of BaSr₅Lu_1,6Ho_0,4W₃□O₁₈ the compounds crystallize in a rhombohedral 18 L type with the sequence (hhcccc)₃; space group R3 m. The refined, intensity related R' value is 11.5%. The differences in properties (diffuse reflectance spectra, photoluminescence) between the hexagonal modifications Ba₆B_2?y³⁺SE_y³⁺W₃□O₁₈ (B³⁺ ? Gd, Y, Lu; SE³⁺ ? Sm, Eu, Tb, Dy, Ho, Er, Tm) and the corresponding cubic HT modifications are discussed.     

Color Point Tuning in Lu3−x−yMnxAl5−xSixO12:yCe3+ for White LEDs

A series of the solid‐solution phosphors Lu_3?x?yMn_xAl_5?xSi_xO₁₂:yCe³⁺ is synthesized by solid‐state reaction. The obtained phosphors possess the garnet structure and exhibit similar excitation properties as the phosphor Lu₃Al₅O₁₂:Ce³⁺, but with an effectively improved red component in the emission spectrum. This can be attributed to the energy transfer from Ce³⁺ to Mn²⁺. Our investigation reveals that electric dipole–quadrupole interactions dominate the energy‐transfer mechanism and that the critical distance determined by the spectral overlap method is about 9.21 Å. The color‐tunable emissions of the Lu_3?x?yMn_xAl_5?xSi_xO₁₂:yCe³⁺ phosphor as a function of Mn₃Al₂Si₃O₁₂ content are realized by continuously shifting the chromaticity coordinates from (0.354, 0.570) to (0.462, 0.494). They indicate that the obtained material may have potential application as a blue radiation‐converting phosphor for white LEDs with high‐quality white light.     

Targeting Vacancies in Nitridosilicates: Aliovalent Substitution of M2+ (M=Ca,Sr) by Sc3+ and U3+

Based on the known linking options of their fundamental building unit, that is the SiN₄ tetrahedron, nitridosilicates belong to the inorganic compound classes with the greatest structural variability. Although facilitating the discovery of novel Si–N networks, this variability represents a challenge when targeting non‐stoichometric compounds. Meeting this challenge, a strategy for targeted creation of vacancies in highly condensed nitridosilicates by exchanging divalent M²⁺ for trivalent M³⁺ using the ion exchange approach is reported. As proof of concept, the first Sc and U nitridosilicates were prepared from α‐Ca₂Si₅N₈ and Sr₂Si₅N₈. Powder X‐ray diffraction (XRD) and synchrotron single‐crystal XRD showed random vacancy distribution in Sc_0.2Ca_1.7Si₅N₈, and partial vacancy ordering in U_0.5xSr_2?0.75xSi₅N₈ with x≈1.05. The high chemical stability of U nitridosilicates makes them interesting candidates for immobilization of actinides.     

Targeting Vacancies in Nitridosilicates: Aliovalent Substitution of M2+ (M=Ca,Sr) by Sc3+ and U3+

Based on the known linking options of their fundamental building unit, that is the SiN₄ tetrahedron, nitridosilicates belong to the inorganic compound classes with the greatest structural variability. Although facilitating the discovery of novel Si–N networks, this variability represents a challenge when targeting non‐stoichometric compounds. Meeting this challenge, a strategy for targeted creation of vacancies in highly condensed nitridosilicates by exchanging divalent M²⁺ for trivalent M³⁺ using the ion exchange approach is reported. As proof of concept, the first Sc and U nitridosilicates were prepared from α‐Ca₂Si₅N₈ and Sr₂Si₅N₈. Powder X‐ray diffraction (XRD) and synchrotron single‐crystal XRD showed random vacancy distribution in Sc_0.2Ca_1.7Si₅N₈, and partial vacancy ordering in U_0.5xSr_2?0.75xSi₅N₈ with x≈1.05. The high chemical stability of U nitridosilicates makes them interesting candidates for immobilization of actinides.     

Pr10[Si10−xAlxO9+xN17−x]Cl with x ≈ 1 – an Oxonitridoaluminosilicate Chloride

The oxonitridoaluminosilicate chloride Pr₁₀[Si_10?xAl_xO_9+xN_17?x]Cl was obtained by the reaction of praseodymium metal, the respective chloride, AlN and Al(OH)₃ with “Si(NH)₂” in a radiofrequency furnace at temperatures around 1900 °C. The crystal structure was determined by single‐crystal X‐ray diffraction (Pbam, no. 55, Z = 2,a = 10.5973(8) Å, b = 11.1687(6) Å, c = 11.6179(7) Å, R1 = 0.0337). The sialon crystallizes isotypically to the oxonitridosilicate halides Ce₁₀[Si₁₀O₉N₁₇]Br, Nd₁₀[Si₁₀O₉N₁₇]Br and Nd₁₀[Si₁₀O₉N₁₇]Cl, which represent a new layered structure type. The structure refinement was performed utilizing an O/N‐distribution model according to Paulings rules, i.e. nitrogen was positioned on all bridging sites and mixed O/Noccupation was assumed on the terminal sites resulting in charge neutrality of the compounds. The Si and Al atoms were refined equally distributed on their three crystallographic sites, due to their poor distinguishability by X‐ray analysis. The tetrahedra layers of the structure consist of condensed [(Si,Al)N₂(O,N)₂] and [(Si,Al)N₃(O,N)] tetrahedra of Q² and Q³ type. The chemical composition of the compound was derived from electron probe micro analyses (EPMA).     

Red and yellow solvates of chloro­(2,2′:6′,2′′‐terpyridine)platinum(II) chloride and Pt⋯Pt inter­actions

Crystallization of chloro­(2,2′:6′,2′′‐terpyridine)platinum(II) chloride from dimethyl sulfoxide yields a red polymorph, [PtCl(C₁₅H₁₁N₃)]Cl·C₂H₆OS, (I), which exhibits stacking along the a axis through pairs of Pt⋯Pt(−x, −y, −z) inter­actions of 3.3155 (8) Å. The cations are further associated through close Pt⋯Pt(1 − x, −y, −z) distances of 3.4360 (8) Å. Recrystallization from water gives a mero­hedrally twinned yellow–orange dihydrate form, [PtCl(C₁₅H₁₁N₃)]Cl·2H₂O, (II), with pairwise short Pt⋯Pt(1 − x, 2 − y, −z) contacts of 3.3903 (5) Å but no long‐range stacking through the crystals. Inter­pair Pt⋯Pt(−x, 2 − y, −z) distances between cation pairs in the hydrate are 4.3269 (5) Å.     

Synthesis and crystal structures of RE7Zn21+xSi2–x [RE = Ce,Pr, and Nd; 0.09 (1) < x < 0.95 (1)]

The focus of this paper is on the synthesis and crystal structures of three Zn‐rich compounds with the general formula RE₇Zn_21+xSi_2−x, where RE = Ce [x = 0.95 (1); heptacerium docosazinc silicon], Pr [x = 0.09 (1); heptapraseodymium henicosazinc disilicon], and Nd [x = 0.53 (1); heptaneodymium docosazinc silicon]. The compounds were obtained by high‐temperature reactions, using the respective elements as starting materials. The structures were determined by single‐crystal X‐ray diffraction. The title compounds crystalize in the orthorhombic space group Pbam (No. 55, Pearson symbol oP60) and are isostructural with about a dozen RE₇Zn_21+xTt_2−x (RE = La–Nd; Tt = Ge, Sn, and Pb) compounds previously reported by our group. The results from the present refinements confirm the previously published data on RE₇Zn_21+xSi_2−x (RE = La and Ce; x≃ 1.45) [Malik et al. (2013). Intermetallics, 36 , 118–126]. Additionally, magnetic susceptibility measurements on the corresponding bulk samples show Curie–Weiss paramagnetic behavior from 5 to 300 K, consistent with RE³⁺ ground states and local‐moment magnetism due to the core 4f electrons.     

Über hexagonale Perowskite mit Kationenfehlstellen. XXXII. Die Photolumineszenz der dreiwertigen Seltenen Erden in den Systemen Ba2−ySryLa2−xSExMgW2□O12

On Hexagonal Perovskites with Cationic Vacancies. XXXII. Photoluminescence of Trivalent Rare Earth in the Systems Ba_2?ySr_yLa_2?xRE_xMgW₂□O₁₂ In the series Ba_2?ySr_yLa_2?xRE_xMgW₂□O₁₂ the Ba²⁺ can be completely substituted by Sr²⁺. All compounds crystallize in the rhombohedral 12 L-type (space group R3 m; sequence (hhcc)₃). By doping the stacking polytypes with some of the trivalent rare earths efficient visible photoluminescence is obtained. The simultaneous incorporation of two different rare earth ions leads to two-color-phosphors, which, according to the excitation energy used, emit either mainly the typical spectrum from one or the other activator; the corresponding luminescence mechanism are discussed.     

Barium‐deficient celsian,Ba1−xAl2−2xSi2+2xO8 (x = 0.20 or 0.06)

Barium‐deficient forms of celsian (barium aluminium silicate) with the formula Ba_1−xAl_2−2xSi_2+2xO₈ (x = 0.20 and 0.06) have been identified. In contrast with the celsian–orthoclase solid solutions which have been reported previously, these forms, refined in the space group C2/m, with Ba and one O atom in the 4i sites with m site symmetry, and a further O atom in a 4g site with twofold axial symmetry, suggest a slight solid solution with silica. The serendipitous preparation of the compounds represents a possible hazard associated with solid‐state synthesis.     

Synthesis,crystal structures and chemical bonding of RE5−xLixGe4 (RE = Nd,Sm and Gd; x≃ 1) with the orthorhombic Gd5Si4 type

The syntheses and single‐crystal and electronic structures of three new ternary lithium rare earth germanides, RE_5−xLi_xGe₄ (RE = Nd, Sm and Gd; x≃ 1), namely tetrasamarium lithium tetragermanide (Sm_3.97Li_1.03Ge₄), tetraneodymium lithium tetragermanide (Nd_3.97Li_1.03Ge₄) and tetragadolinium lithium tetragermanide (Gd_3.96Li_1.03Ge₄), are reported. All three compounds crystallize in the orthorhombic space group Pnma and adopt the Gd₅Si₄ structure type (Pearson code oP36). There are six atoms in the asymmetric unit: Li1 in Wyckoff site 4c, RE1 in 8d, RE2 in 8d, Ge1 in 8d, Ge2 in 4c and Ge3 in 4c. One of the RE sites, i.e. RE2, is statistically occupied by RE and Li atoms, accounting for the small deviation from ideal RE₄LiGe₄ stoichiometry.     

Darstellung und Kristallstrukturen von Li4−2xSr2+xB10S19 (x ≈ 0,27) und Na6B10S18. Zwei neue Thioborate mit hochpolymeren Makrotetraeder-Netzwerken

Synthesis and Crystal Structures of Li_4?2xSr_2+xB₁₀S₁₉ (x ≈ 0.27) and Na₆B₁₀S₁₈. Two Novel Thioborates with Highly Polymeric Macro-tetrahedral Networks Li_4?2xSr_2+xB₁₀S₁₉ (x ≈ 0.27) and Na₆B₁₀S₁₈ were prepared from the reaction of strontium sulfide and lithium sulfide (sodium sulfide) with boron and sulfur at 700°C in graphitized silica tubes. Li_4?2xSr_2+xB₁₀S₁₉ (x ≈ 0.27) crystallizes in the monoclinic space group P2₁/c with a = 10.919(2) Å, b = 13.590(3) Å, c = 16.423(4) Å, and β = 90.48(2)°, Na₆B₁₀S₁₈ in the tetragonal space group I4₁/acd with a = 14.415(3) Å, c = 26.137(4) Å. Both structures contain supertetrahedral B₁₀S₂₀ units which are linked through tetrahedral corners to form a three-dimensional polymeric network in the case of Na₆B₁₀S₁₈ and one-dimensional chains in the case of Li_4?2xSr_2+xB₁₀S₁₉ (x ≈ 0.27). All boron atoms are in tetrahedral BS₄ coordination (B? S bond lengths vary from 1.879(5) to 1.951(5) Å (1.875(10) to 1.987(9) Å)). The strontium and lithium (sodium) cations are located within large channels formed by the anions.     

Sr5Ge2N6 – A Nitridogermanate with Edge‐sharing Double Tetrahedra

The new nitridogermanate Sr₅Ge₂N₆ was obtained as a coarsely crystalline product by Na‐flux technique employing a reaction of Sr, Na, NaN₃ and GeO₂ in weld shut tantalum‐tubes at temperatures up to 760 °C. The crystal structure was determined by single‐crystal X‐ray methods: (Sr₅Ge₂N₆, space group C2/c (no. 15), a = 1040.8(2), b = 652.08(13), c = 1356.5(3) pm, β = 100.29(3)°, V = 905.8(3)·10⁶ pm³, Z = 4, 1240 observed reflections, 61 parameters, R1 = 0.031). In the solid, there are edge‐sharing [Ge₂N₆]¹⁰⁻ double tetrahedra surrounded by Sr²⁺ ions. Sr₅Ge₂N₆ was found to be isotypic with Ca₅Si₂N₆.     

Structural Variations in the Solid‐Solution Series LnxCa2−xAl[Al1+xSi1−xO7] with 0 ≤ x ≤ 1 and Ln = La,Eu, Er

Gehlenite, Ca₂Al[AlSiO₇], has melilite‐type structure with space group . It contains two topologically distinct positions coordinated tetrahedrally by oxygen. One is completely occupied by Al³⁺, whereas the other one contains Al³⁺ and Si⁴⁺. Normally, the Al³⁺ molar fraction in the second tetrahedrally coordinated position does not exceed x_Al = 0.5, i.e. the so‐called Loewenstein‐rule is obeyed. In this contribution the structural variations in the melilite‐type compounds of the compositions La_xCa_2?xAl[Al_1+xSi_1?xO₇], Eu_xCa_2?xAl[Al_1+xSi_1?xO₇] and Er_xCa_2?xAl[Al_1+xSi_1?xO₇] are discussed. All members of the solid solution except the end‐members violate Loewenstein's rule. Rietveld refinements against X‐ray powder diffraction patterns confirm that the compounds have space group , without changes in the Wyckoff‐positions of the ions compared to gehlenite.     

A Naphthalene-Like Si1010− Unit in the Novel ∞2[Si2030−] Planar Anion of Sr13Mg2Si20

Two interpenetrating ² _∞ [Si ₂₀ ³⁰⁻ ] polyanions with naphthalene-like Si₁₀¹⁰⁻ building blocks (see picture) characterize the“nonclassical” Zintl phase Sr₁₃Mg₂Si₂₀, which is formed from the elements at 1230–1240 K. The ecliptical stacking of the Si₁₀¹⁰⁻ units leads to one-dimensional conductivity along the stacking direction.     

Über hexagonale Perowskite mit Kationenfehlstellen. XXVII. Die Systeme Ba4−xSrxBIIRe2□O12′, Ba4BCaxRe2□O12 und Ba4−xLaxBIIRe2−xWx□O12 mit BII = Co,Ni

On Hexagonal Perovskites with Cationic Vacancies. XXVII. Systems Ba_4?xSr_xB^IIRe₂□O₁₂, Ba₄B Ca_xRe₂□O₁₂, and Ba_4?xLa_xB^IIRe_2?xW_x□O₁₂ with B^II = Co, Ni In the systems Ba_4?xSr_xB^IIRe₂□O₁₂, Ba₄BCa_xRe₂□O₁₂ and Ba_4?xLa_xB^IIRe_2?xW_x□O₁₂ (B^II = Co, Ni) hexagonal perovskites with a rhombohedral 12 L structure (general composition A₄BM₂□O₁₂; sequence (hhcc)₃; space group R&3macr;m) are observed. With the exception of Ba₄NiRe₂□O₁₂ the octahedral net consists of BO₆ single octahedra and M₂□O₁₂ face connected blocks (type 1). In type 2 (Ba₄NiRe₂□O₁₂) the M ions are located in the single octahedra and in the center of the groups of three face connected octahedra. The two outer positions of the latter are occupied by B ions and vacancies in the ratio 1:1. The difference between type 1 and 2 are discussed by means of the vibrational and diffuse reflectance spectra.     

The Sialons MLn[Si4−xAlxOxN7−x] with M = Eu,Sr, Ba and Ln = Ho‐Yb – Twelve Substitution Variants with the MYb[Si4N7] Structure Type

The oxonitridoalumosilicates (so‐called sialons) MLn[Si_4?xAl_xO_xN_7?x] with M = Eu, Sr, Ba and Ln =Ho, Er, Tm, Yb were obtained by the reaction of the respective lanthanoid metal, the alkaline earth carbonates or europium carbonate, resp., AlN, “Si(NH)₂” and MCl₂ as a flux in a radiofrequency furnace at temperatures around 2100 °C. The compounds MLn[Si_4?xAl_xO_xN_7?x] are relevant for the investigation of substitutional effects on the materials properties due to their ability of tolerating a comparatively large phase width up to x ≈ 2.0(5). The crystal structures of the twelve compounds were refined from X‐ray single crystal data and X‐ray powder data and are found to be isotypic to the MYb[Si₄N₇] structure type. The compounds crystallize in space group P6₃mc (no. 186, hexagonal) and are made up of chains of so‐called starlike units [N^[4](SiN₃)₄] or [N^[4]((Si,Al)(O,N)₃)₄], respectively. These units are formed by four (Si,Al)(N/O)₄ tetrahedra sharing a common central nitrogen atom. The structure refinement was performed utilizing an O/N‐distribution model according to Paulings rules, i.e. nitrogen was positioned on the four‐fold bridging site and nitrogen and oxygen were distributed equally on both of the two‐fold bridging sites, resulting in charge neutrality of the compound. The Si and Al atoms were distributed equally on their two crystallographic sites, referring to their elemental proportion in the compound, due to being poorly distinguishable by X‐ray methods. The chemical compositions of the compounds were derived from electron probe micro analyses (EPMA).     

Synthesis,Persistent Luminescence,and Thermoluminescence Properties of Yellow Sr3SiO5:Eu2+,RE3+ (RE=Ce,Nd, Dy,Ho, Er,Tm, Yb) and Orange‐Red Sr3−xBaxSiO5:Eu2+, Dy3+ Phosphor

Sunlight‐excitable orange or red persistent oxide phosphors with excellent performance are still in great need. Herein, an intense orange‐red Sr_3?xBa_xSiO₅:Eu²⁺,Dy³⁺ persistent luminescence phosphor was successfully developed by a two‐step design strategy. The XRD patterns, photoluminescence excitation and emission spectra, and the thermoluminescence spectra were investigated in detail. By adding non‐equivalent trivalent rare earth co‐dopants to introduce foreign trapping centers, the persistent luminescence performance of Eu²⁺ in Sr₃SiO₅ was significantly modified. The yellow persistent emission intensity of Eu²⁺ was greatly enhanced by a factor of 4.5 in Sr₃SiO₅:Eu²⁺,Nd³⁺ compared with the previously reported Sr₃SiO₅:Eu²⁺, Dy³⁺. Furthermore, Sr ions were replaced with equivalent Ba to give Sr_3?xBa_xSiO₅:Eu²⁺,Dy³⁺ phosphor, which shows yellow‐to‐orange‐red tunable persistent emissions from λ=570 to 591 nm as x is increased from 0 to 0.6. Additionally, the persistent emission intensity of Eu²⁺ is significantly improved by a factor of 2.7 in Sr_3?xBa_xSiO₅:Eu²⁺,Dy³⁺ (x=0.2) compared with Sr₃SiO₅:Eu²⁺,Dy³⁺. A possible mechanism for enhanced and tunable persistent luminescence behavior of Eu²⁺ in Sr_3?xBa_xSiO₅:Eu²⁺,RE³⁺ (RE=rare earth) is also proposed and discussed.     

Neue Vertreter des Er6[Si11N20]O‐Strukturtyps Hochtemperatur‐Synthesen und Kristallstrukturen von Ln(6+x/3)[Si(11–y)AlyN(20+x–y)]O(1–x+y) mit Ln = Nd,Er, Yb,Dy und 0 ≤ x ≤ 3, 0 ≤ y ≤ 3

New Representatives of the Er₆[Si₁₁N₂₀]O Structure Type. High‐Temperature Synthesis and Single‐Crystal Structure Refinement of Ln_(6+x/3)[Si_(11–y)Al_yN_(20+x–y)]O_(1–x+y) with Ln = Nd, Er, Yb, Dy and 0 ≤ x ≤ 3, 0 ≤ y ≤ 3 According to the general formula Ln_(6+x/3)[Si_(11–y)Al_yN_(20+x–y)]O_(1–x+y) (0 ≤ x ≤ 3, 0 ≤ y ≤ 3) four nitridosilicates, namely Er₆[Si₁₁N₂₀]O, Yb_6.081[Si₁₁N_20.234]O_0.757, Dy_0.33Sm₆[Si₁₁N₂₀]N, and Nd₇[Si₈Al₃N₂₀]O were synthesized in a radiofrequency furnace at temperatures between 1300 and 1650 °C. The homeotypic crystal structures of all four compounds were determined by single‐crystal X‐ray diffraction. The nitridosilicates are trigonal with the following lattice constants: Er₆[Si₁₁N₂₀]O: a = 978.8(4) pm, c = 1058.8(3) pm; Yb_6.081[Si₁₁N_20.243]O_0.757: a = 974.9(1) pm, c = 1055.7(2) pm; Dy_0.33Sm₆[Si₁₁N₂₀]N: a = 989.8(1) pm, c = 1078.7(1) pm; Nd₇[Si₈Al₃N₂₀]O: a = 1004.25(9) pm, c = 1095.03(12) pm. The crystal structures were solved and refined in the space group P31c with Z = 2. The compounds contain three‐dimensional networks built up by corner sharing SiN₄ and AlN₄ tetrahedra, respectively. The Ln³⁺ and the “isolated” O^2– ions are situated in the voids of the structures. According to Ln_(6+x/3)[Si_(11–y)Al_yN_(20+x–y)]O_(1–x+y) an extension of the Er₆[Si₁₁N₂₀]O structure type has been found.     

Unexpected Luminescence Properties of Sr0.25Ba0.75Si2O2N2:Eu2+—A Narrow Blue Emitting Oxonitridosilicate with Cation Ordering

Owing to a parity allowed 4f⁶(⁷F)5d¹→4f⁷(⁸S_7/2) transition, powders of the nominal composition Sr_0.25Ba_0.75Si₂O₂N₂:Eu²⁺ (2 mol % Eu²⁺) show surprising intense blue emission (λ_em=472 nm) when excited by UV to blue radiation. Similarly to other phases in the system Sr_1?xBa_xSi₂O₂N₂:Eu²⁺, the described compound is a promising phosphor material for pc‐LED applications as well. The FWHM of the emission band is 37 nm, representing the smallest value found for blue emitting (oxo)nitridosilicates so far. A combination of electron and X‐ray diffraction methods was used to determine the crystal structure of Sr_0.25Ba_0.75Si₂O₂N₂:Eu²⁺. HRTEM images reveal the intergrowth of nanodomains with SrSi₂O₂N₂ and BaSi₂O₂N₂‐type structures, which leads to pronounced diffuse scattering. Taking into account the intergrowth, the structure of the BaSi₂O₂N₂‐type domains was refined on single‐crystal diffraction data. In contrast to coplanar metal atom layers which are located between layers of condensed SiON₃‐tetrahedra in pure BaSi₂O₂N₂, in Sr_0.25Ba_0.75Si₂O₂N₂:Eu²⁺ corrugated metal atom layers occur. HRTEM image simulations indicate cation ordering in the final structure model, which, in combination with the corrugated metal atom layers, explains the unexpected and excellent luminescence properties.     

Strontium magnesium phosphate,Sr2+xMg3−xP4O15 (x∼ 0.36), from laboratory X‐ray powder data

The previously unknown crystal structure of strontium magnesium phosphate, Sr_2+xMg_3−xP₄O₁₅ (x∼ 0.36), determined and refined from laboratory powder X‐ray diffraction data, represents a new structure type. The title compound was synthesized by high‐temperature solid‐state reaction and it crystallizes in the orthorhombic space group Cmcm. It was earlier thought to be stoichiometric Sr₂Mg₃P₄O₁₅, but our structural study indicates the nonstoichiometric composition. The asymmetric unit contains one Sr (site symmetry ..m on special position 8g), one M (= Mg 64%/Sr 36%; site symmetry 2/m.. on special position 4b), one Mg (site symmetry 2.. on special position 8e), two P (site symmetry m.. on special position 8f and site symmetry ..m on special position 8g), and six O sites [two on general positions 16h, two on 8g, one on 8f and one on special position 4c (site symmetry m2m)]. The nonstoichiometry is due to the mixing of magnesium and strontium ions on the M site. The structure consists of three‐dimensional networks of MgO₄ and PO₄ tetrahedra, and MO₆ octahedra with the other strontium ions occupying the larger cavities surrounded by ten O atoms. All the polyhedra are connected by corner‐sharing except the edge‐sharing MO₆ octahedra forming one‐dimensional arrangements along [001].