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Local Structure and Luminescence Tuning in Phosphors
Published in Ru-Shi Liu, Xiao-Jun Wang, Phosphor Handbook, 2022
Alkaline-earth metal orthosilicate phosphors M2SiO4:Eu2+ (M = Sr, Ba) have aroused wide research interests in wLED applications. Its luminescence was first reported by Barry in 1968.[86] Among this silicate series, Ba2SiO4 and high-temperature phase α-Sr2SiO4 belong to the β-K2SO4-type orthorhombic crystal system with space group Pmnb. [87,88] Two cation sites exist: ten-coordinated M1 site and nine-coordinated M2 site. Denault et al. reported the dependence of thermal luminescent stability on the composition in (Ba1−xSrx)2SiO4:Eu2+ phosphors, drawing the conclusion that the intermediate composition with 46% Sr has the highest resistance to the thermal quenching of luminescence and ascribed this to optimal bonding that creates a more rigid crystal structure compared to the end-member compositions. [3]
Factors Controlling Lifetimes of Polyhydroxyalkanoates and their Composites in the Natural Environment
Published in Martin Koller, The Handbook of Polyhydroxyalkanoates, 2020
Bronwyn Laycock, Steven Pratt, Alan Werker, Paul A. Lant
In studies on drawn PHB and PHBV fibers, X-ray patterns showed reflections from both the usual α-form (an orthorhombic crystal system with a 21 helix conformation space) and the β-form (with a planar zigzag conformation) simultaneously. The enzymatic erosion rate of the β-form was found to be much faster in comparison with the α-form [62,66,67].
Oxide Based Supercapacitors I-Manganese Oxides
Published in Ling Bing Kong, Nanomaterials for Supercapacitors, 2017
Ling Bing Kong, Wenxiu Que, Lang Liu, Freddy Yin Chiang Boey, Zhichuan J. Xu, Kun Zhou, Sean Li, Tianshu Zhang, Chuanhu Wang
The broad diffraction peaks of the pattern for the ramsdellite as shown in Fig. 4.11(d) were attributed to the presence of stacking faults in the structure of the sample [6, 53]. It belonged to the orthorhombic crystal system, with unit cell parameters of a = 9.273 Å, b = 2.866 Å and c = 4.533 Å, as well as space group Pnma [6]. According to Fig. 4.11(e), the Ni-todorokite MnO2 exhibited a 3 × 3 tunnel structure, with a monoclinic crystal structure, having space group P2/m and unit cell parameters of a = 9.757 Å, b = 2.842 Å, c = 9.560 Å and β = 94.07° [47,48,54].
Cu(II) coordination polymers stabilized by pyridine-2,6-dicarboxylate anion and pyrazole derivatives through ligand hydrolysis
Published in Journal of Coordination Chemistry, 2018
Ezzat Khan, Sher Ali Khan, Muhammad Zahoor, Muhammad Nawaz Tahir, Awal Noor, Ataf Ali Altaf
The molecular structure of 7 is shown in Figure 5 together with selected bond lengths and angles. The corresponding data related to crystal structure determination are summarized in Table 1. Compound 7 crystallizes in space group P212121, an orthorhombic crystal system. The Cu ion adopts distorted square pyramidal geometry. The pyridine-2,6-dicarboxylate ligand is linked to the metal center through ONO in a tridentate fashion, in a similar way as in 6. The ONO of the 2,6-pyridinedicarboxylate anion and N atom of 3-methylpyrazole group are coplanar and constitute a square plane around the copper ion within experimental limits [26]. The sum of angles between atoms constituting the square plane of the molecule is 359.4°, which is very close to a perfect planar geometry (∠N3–Cu1–O2 99.8°, ∠N1–Cu1–O2 81.0°, ∠N1–Cu1–O1 79.5°, ∠N3–Cu1–O1 99.1°). The difference in bond angles is obvious because of the strained structure of the pincer 2,6-pyridinedicarboxylate ligand. The oxygen atom O4 from the neighboring molecule occupies the axial position making a square pyramidal arrangement around the metal atom. All bond angles between CuO4 atoms of the square plane (O1,N1,O2,N3) range from 88.39 – 98.26°. The Cu–N and Cu–O bond distances are within the expected limit, i.e. Cu1–N1 1.916 Å, Cu1–N3 1.940 Å, Cu1–O2 2.020 Å, and Cu1–O1 2.073 Å. The Cu1–O4 distance is considerably longer (2.210 Å) than the Cu1–O2 and Cu1–O1 (see caption of Figure 5). The distances between C and O atoms of the ligand are O3–C7 1.253 Å, O2–C1 1.278 Å and O4–C1 1.231 Å, and thus show electronic delocalization among these atoms. The elongation of the O3–C7 bond compared to the C = O in free ligand shows the flow of electron density to the metal center. The individual molecules are bridged through a C = O moiety and extends the structure in a zigzag 1D manner as shown in Figure 6.