Due to the relationship between structure and luminescence properties, detailed crystal structure determination for microcrystalline phosphors is necessary for a profound understanding of materials properties. The yellow phosphor La 3 BaSi 5 N 9 O 2 :Ce 3+ (λ max = 578 nm; fwhm ∼4700 cm −1 ) was characterized by a combination of transmission electron microscopy (TEM) and synchrotron microfocus diffraction as only agglomerates of crystals with a maximum size of a few μm could be obtained yet. La 3 BaSi 5 N 9 O 2 :Ce 3+ was synthesized from LaF 3 , La(NH 2 ) 3 , BaH 2 , Si(NH) 2 , and CeF 3 in a radio frequency furnace. It crystallizes in space group Pmn2 1 (no. 31) with a = 9.5505(8), b = 19.0778(16), c = 12.1134(9) Å, and Z = 8. Its interrupted three-dimensional tetrahedra network contains zehner and dreier rings of vertex-sharing SiN 4 and SiN 2 O 2 tetrahedra. The crystal structure was confirmed by high-resolution TEM and Z-contrast scanning TEM. The element distribution was derived by bond-valence sum calculations. The infrared spectrum proves the absence of N−H bonds.

The first gallium-containing nitridosilicate CaGaSiN was synthesized in newly developed high-pressure autoclaves using supercritical ammonia as solvent and nitriding agent. The reaction was conducted in an ammonobasic environment starting from intermetallic CaGaSi with NaN as a mineralizer. At 770 K, intermediate compounds were obtained, which were subsequently converted to the crystalline nitride at temperatures up to 1070 K (70-150 MPa). The impact of other mineralizers (e.g., LiN , KN , and CsN ) on the product formation was investigated as well. The crystal structure of CaGaSiN was analyzed by powder X-ray diffraction and refined by the Rietveld method. The structural results were further corroborated by transmission electron microscopy, Si MAS-NMR, and first-principle DFT calculations. CaGaSiN crystallizes in the orthorhombic space group Cmc2 (no. 36) with lattice parameters a=9.8855(11), b=5.6595(1), c=5.0810(1) Å, (Z=4, R =0.0326), and is isostructural with CaAlSiN (CASN). Eu doped samples exhibit red luminescence with an emission maximum of 620 nm and FWHM of 90 nm. Thus, CaGaSiN :Eu also represents an interesting candidate as a red-emitting material in phosphor-converted light-emitting diodes (pc-LEDs). In addition to the already known substitution of alkaline-earth metals in (Ca,Sr)AlSiN :Eu , inclusion of Ga is a further and promising perspective for luminescence tuning of widely used red-emitting CASN type materials.

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In the system Ge-Sn-Sb-Te, there is a complete solid solution series between GeSb2Te4 and SnSb2Te4. As Sn2Sb2Te5 does not exist, Sn can only partially replace Ge in Ge2Sb2Te5; samples with 75% or more Sn are not homogeneous. The joint refinement of high-resolution synchrotron data measured at the K-absorption edges of Sn, Sb and Te combined with data measured at off-edge wavelengths unambiguously yields the element distribution in 21R-Ge(0.6)Sn(0.4)Sb2Te4 and 9P-Ge(1.3)Sn(0.7)Sb2Te5. In both cases, Sb predominantly concentrates on the position near the van der Waals gaps between distorted rocksalt-type slabs whereas Ge prefers the position in the middle of the slabs. No significant antisite disorder is present. Comparable trends can be found in related compounds; they are due to the single-side coordination of the Te atoms at the van der Waals gap, which can be compensated more effectively by Sb(3+) due to its higher charge in comparison to Ge(2+). The structure model of 21R-Ge(0.6)Sn(0.4)Sb2Te4 was confirmed by high-resolution electron microscopy and electron diffraction. In contrast, electron diffraction patterns of 9P-Ge(1.3)Sn(0.7)Sb2Te5 reveal a significant extent of stacking disorder as evidenced by diffuse streaks along the stacking direction. The Seebeck coefficient is unaffected by the Sn substitution but the thermal conductivity drops by a factor of 2 which results in a thermoelectric figure of merit ZT = ~0.25 at 450 °C for both Ge(0.6)Sn(0.4)Sb2Te4 and Ge(1.3)Sn(0.7)Sb2Te5, which is higher than ~0.20 for unsubstituted stable layered Ge-Sb-Te compounds.

Thorough investigation of nitridophosphates has rapidly accelerated through development of new synthesis strategies. Here we used the recently developed high-pressure metathesis to prepare the first rare-earth metal nitridophosphate, CeLiPN, with a high degree of condensation >1/2. CeLiPN consists of an unprecedented hexagonal framework of PN tetrahedra and exhibits blue luminescence peaking at 455 nm. Transmission electron microscopy (TEM) revealed two intergrown domains with slight structural and compositional variations. One domain type shows extremely weak superstructure phenomena revealed by atomic-resolution scanning TEM (STEM) and single-crystal diffraction using synchrotron radiation. The corresponding superstructure involves a modulated displacement of Ce atoms in channels of tetrahedra 6-rings. The displacement model was refined in a supercell as well as in an equivalent commensurate (3 + 2)-dimensional description in superspace group P6(α, β, 0)0(-α - β, α, 0)0. In the second domain type, STEM revealed disordered vacancies of the same Ce atoms that were modulated in the first domain type, leading to sum formula CeLiPNO (x ≈ 0.72) of the average structure. The examination of these structural intricacies may indicate the detection limit of synchrotron diffraction and TEM. We discuss the occurrence of either Ce displacements or Ce vacancies that induce the incorporation of O as necessary stabilization of the crystal structure.