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Significant oxide-ionic conductivity has been recently reported for a family of cation-deficient hexagonal perovskite derivatives Ba3M2O8.5 (M = Mo/W6+ and Nb5+/V5+). Herein, strong 4-fold coordination geometry preferring Ge4+ ions are doped into Ba3Mo1+xNb1−2xGexO8.5 to manipulate the oxygen distribution within palmierite-like layers for the enhancement of oxide-ionic conductivity. Rietveld refinement of the neutron diffraction data of Ba3Mo1.2Nb0.6Ge0.2O8.5 reveals that Ge4+-ions are selectively incorporated into the palmierite-like layers, owing to their strong 4-fold coordination environment preference. Such a site-selective doping behavior leads to an increase in the occupation proportion of the O3 site and a concomitant decrease in the occupancy factor for O2. Ionic conduction measurements show that the bulk conductivity of Ba3Mo1.2Nb0.6Ge0.2O8.5 is about twice higher than that of the parent compound at intermediate temperatures (300–500 °C). Furthermore, bond-valence site energy (BVSE) landscape analysis reveals that the oxygen ionic conduction of Ba3Mo1+xNb1−2xGexO8.5 is dominated by the two-dimensional pathways along the palmierite-like layers, despite the three-dimensional (3D) oxygen diffusion pathways being present in the hybrid structure, which strongly confirms that the enhancement in ionic conductivity at intermediate temperatures is attributed to the site-selective Ge4+-substitution-induced redistribution of oxygen ions within the palmierite-like layers. [ABSTRACT FROM AUTHOR]

Recently, broad-band white-light-emitting using Eu2+, Ce3+, or Bi3+ in multi-sites of a single-phase phosphor have drawn extensive attention due to their potential to realize high-quality indoor lighting. This work reports a novel oxide, Ca7Mg2Ga6O18 (CMG), possessing a complex crystal structure in the space group F432. Rietveld refinements of high-resolution synchrotron X-ray diffraction data were performed to determine the accurate atomic positions and occupancy factors, giving a reasonable composition of Ca7Mg1.91(4)Ga6.09(4)O18. Due to the multiple sites of Ca2+, which are suitable for the doping of Bi3+ activators, CMG is a promising host to achieve broad-band white-light emission. Detailed structural and spectroscopic analyses revealed that the Bi3+-activator shows multiple and site-selective occupancy, which is the origin of the red-shifts in both broad-band excitation and emission spectra upon increasing the Bi3+ content. A series of Bi3+ and Eu3+ codoped phosphors with tunable blue-pink-red emission were prepared due to the Bi3+-to-Eu3+ energy transfer. Due to the distinctive thermal behaviors of Bi3+ and Eu3+ emissions, CMG:Bi3+,Eu3+ is a candidate for optical thermometry. [ABSTRACT FROM AUTHOR]

The crystal structures, photoluminescence properties, and transport properties of a series of new "114" oxides CaBa1−xSrxZn2Al2O7 (x = 0–1) were investigated in detail. Careful Rietveld refinements performed on solid solution samples revealed that the structural symmetry of CaBa1−xSrxZn2Al2O7 evolves from hexagonal P63mc (x < 0.2) to trigonal P31c (0.2 ≤ x ≤ 0.6) and then to orthorhombic Pna21 (x > 0.6) with an increase of the Sr2+-content, which is cooperative with the rotation of T1O4 tetrahedra around the c-axis. Eu3+ was used as a local structural probe to gain an insight into the structure, which further corroborated the correctness of the observed structural symmetry descending sequence in CaBa1−xSrxZn2Al2O7. More importantly, the reduction of structural symmetry is also associated with a tendency from layered ordering to complete charge ordering transition for Zn2+/Al3+ cations, which was revealed to have a significant influence on the transport properties. These findings are expected to offer a route to manipulate the physical properties of "114" oxides containing magnetic cations. [ABSTRACT FROM AUTHOR]

Searching efficient red phosphors under near‐UV or blue light excitation is practically important to improve the current white light‐emitting diodes (WLEDs). Eu2+‐ and Mn4+‐based red phosphors have been extensively studied. Here we proposed that Eu3+ is also a promising activator when it resides on a noncentrosymmetric coordination site. We proved that Cd4GdO(BO3)3 is a good host, which has a significantly distorted coordination for Eu3+. A careful crystallographic study was performed on the solid solutions of Cd4Gd1‐xEuxO(BO3)3 (0≤x≤1) by Rietveld refinements. The as‐doped Eu3+ cations locate at the Gd3+ site and are well separated by CdO8, CdO6 and BO3 groups; thus, only a slight concentration quenching was observed at ≈80 atom % Eu3+. Most importantly, the parity‐forbidden law of 4f‐4f transitions for Eu3+ are severely depressed, thus the absorptions at ≈393 and ≈465 nm are remarkable. Cd4Gd0.2Eu0.8O(BO3)3 can be pumped by a 395 nm LED chip to give a bright red emission, and when mixed with other commercial blue and green phosphors, it can emit the proper white light (0.3657, 0.3613) with a suitable Ra≈87 and correlated colour temperature ≈4326 K. In‐situ photoluminescence study indicated the low thermal quenching of these borate phosphors, especially under 465 nm excitation. Our case proves the practicability to develop near‐UV excited red phosphors in rare‐earth‐containing borates. [ABSTRACT FROM AUTHOR]

Completely B-site-ordered Ba2InTaO6 has been prepared previously by prolonged heating at 1500 °C; here, we significantly lowered the annealing temperature to 1130 °C under H2/Ar dynamic flow and obtained a partially ordered (ca. 74 %) double perovskite, as determined by Rietveld refinement of the powder X-ray diffraction data. As a wide-band-gap semiconductor, Ba2InTaO6 possesses photocatalytic activity for overall water splitting under UV irradiation, though the gas evolution rates of 12.9 and 6.6 μmol/h/g for H2 and O2 generation, respectively, are low. With the assistance of methanol as a sacrificial reagent, the H2 evolution rate increases to 50.5 μmol/h/g, which indicates that the surficial charge recombination rate is really high. We applied the typical cocatalyst-loading method to this material, and with 1 wt.-% PtO x and NiO x, the H2 production rates in pure water were further improved to 16.0 and 18.4 μmol/h/g, respectively. Attempts to dope Ba2InTaO6 with first-row transition metals (Ti, V, Cr, Mn, Fe, Co, and Ni) led to a general enhancement of the light-harvesting ability; however, the experimental water-splitting activity did not improve. We believe that the doped cations most likely behaved as recombination centers for photogenerated charges. Considering its structural similarity to the well-known catalyst InTaO4:Ni, Ba2InTaO6 possesses the potential to extend its photocatalytic activity to the visible-light region but needs further enhancement. [ABSTRACT FROM AUTHOR]

The crystal structures, photoluminescence properties, and transport properties of a series of new "114" oxides CaBa1−xSrxZn2Al2O7 (x = 0–1) were investigated in detail. Careful Rietveld refinements performed on solid solution samples revealed that the structural symmetry of CaBa1−xSrxZn2Al2O7 evolves from hexagonal P63mc (x < 0.2) to trigonal P31c (0.2 ≤ x ≤ 0.6) and then to orthorhombic Pna21 (x > 0.6) with an increase of the Sr2+-content, which is cooperative with the rotation of T1O4 tetrahedra around the c-axis. Eu3+ was used as a local structural probe to gain an insight into the structure, which further corroborated the correctness of the observed structural symmetry descending sequence in CaBa1−xSrxZn2Al2O7. More importantly, the reduction of structural symmetry is also associated with a tendency from layered ordering to complete charge ordering transition for Zn2+/Al3+ cations, which was revealed to have a significant influence on the transport properties. These findings are expected to offer a route to manipulate the physical properties of "114" oxides containing magnetic cations. [ABSTRACT FROM AUTHOR]

Recently, broad-band white-light-emitting using Eu2+, Ce3+, or Bi3+ in multi-sites of a single-phase phosphor have drawn extensive attention due to their potential to realize high-quality indoor lighting. This work reports a novel oxide, Ca7Mg2Ga6O18 (CMG), possessing a complex crystal structure in the space group F432. Rietveld refinements of high-resolution synchrotron X-ray diffraction data were performed to determine the accurate atomic positions and occupancy factors, giving a reasonable composition of Ca7Mg1.91(4)Ga6.09(4)O18. Due to the multiple sites of Ca2+, which are suitable for the doping of Bi3+ activators, CMG is a promising host to achieve broad-band white-light emission. Detailed structural and spectroscopic analyses revealed that the Bi3+-activator shows multiple and site-selective occupancy, which is the origin of the red-shifts in both broad-band excitation and emission spectra upon increasing the Bi3+ content. A series of Bi3+ and Eu3+ codoped phosphors with tunable blue-pink-red emission were prepared due to the Bi3+-to-Eu3+ energy transfer. Due to the distinctive thermal behaviors of Bi3+ and Eu3+ emissions, CMG:Bi3+,Eu3+ is a candidate for optical thermometry. [ABSTRACT FROM AUTHOR]

BiMn x Fe 3- x O 6 ( x = 1) represents a new type of oxide structure containing Bi 3+ and competing magnetic super-exchanges. In literature, multiple magnetic states were realized at low temperatures in BiMnFe 2 O 6 , and the hypothetical parent compounds (BiMn 3 O 6 , BiFe 3 O 6 ) were predicted to be different in magnetism. Herein, we performed a careful study on the syntheses of BiMn x Fe 3- x O 6 at ambient pressure, and the solid solution range was determined to be 0.9 ≤ x ≤ 1.3 by Rietveld refinements on high-quality powder X-ray diffraction data. Due to the very similar cationic size of Mn 3+ and Fe 3+ , and possibly the structural rigidity, there was no significant structure change in the whole range of solid solution. The magnetic behavior of BiMn x Fe 3- x O 6 ( x = 1.2, 1.22, 1.26, 1.28 and 1.3) was generally similar to BiMnFe 2 O 6 , while the relative higher concentration of Mn 3+ led to the decreasing of the antiferromagnetic ordering temperature. [ABSTRACT FROM AUTHOR]

Temperature-induced phase transitions for stuffed tridymite A Ga 2 O 4 ( A = Sr, Ca) were investigated by experimental and theoretical calculations. A simple annealing of SrCO 3 and Ga 2 O 3 led to the formation of γ-SrGa 2 O 4 ( P 2 1 /n ) below 1200 °C, and transform to β-SrGa 2 O 4 ( P 2 1 /c ) when heated at 1200 °C. A similar phenomenon was found for CaGa 2 O 4 , and the temperature boundary between α-CaGa 2 O 4 ( Pna 2 1 ) and the high temperature polymorph β-CaGa 2 O 4 ( P 2 1 /c ) was about 1350 °C. Rietveld refinements provided detailed structural information for these polymorphs and suggest that the driving force of these phase transitions is the under-bonded nature of the alkaline earth cations. In other words, the need of larger space for Sr 2+ /Ca 2+ in the high temperature β-phase forces the 6-membered-ring channel expand through increasing the Ga-O-Ga angles. Density functional theory calculations proved the formation energies for γ-SrGa 2 O 4 and α-CaGa 2 O 4 were both lower than their high temperature β-polymorphs, in accordance with the experimental observations. [ABSTRACT FROM AUTHOR]

Abstract: New “114” oxides Ca1−x Eu x BaZn2+x Ga2−x O7 (x≤0.24) were synthesized by solid state reaction. Rietveld refinements were performed on high quality powder XRD data in the space group P63 mc. Zn2+ and Ga3+ co-occupy T1 and T2 positions, which are both in tetrahedral coordinated environment. Comparing the host compound, O3 moves towards T2 cation as much as 0.08Å when x=0.24. It is the most observable structural change during the substitution. By comparing the structures of CaBaZn2Ga2O7 (P63 mc) and CaBaCo4O7 (Pbn21), we find that smaller cations in tetrahedral sites would lead to a lower symmetry in “114” oxides. Luminescent spectra show the noncentrosymmetric coordination of Eu3+, and the f–f excitations are comparable to CT-excitation. No concentration quenching was observed up to x=0.24. The optical band gaps were estimated to be 3.8eV for Ca1−x Eu x BaZn2+x Ga2−x O7 (x=0, 0.16). [Copyright &y& Elsevier]

A series of rare earth polyborate with the general formula LiCa RE 5 (BO 3) 6 (RE ​= ​Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y) were synthesized by high temperature solid state reactions. In literature, the Cd-analogues and LiCaTb 5 (BO 3) 6 were reported, here Rietveld refinements were performed on high quality powder X-ray diffraction data and the crystallographic parameters were obtained for the title compounds. Eu3+-luminescence in LiCa RE 5 (BO 3) 6 (RE ​= ​Gd, Y, Lu) were characterized. Eu3+ activators were doped into both the close-to-centrosymmetric and strongly-distorted coordination environments. Overall, bright orange-red emission can be observed with a slight increase of the red-to-orange (R / O) ratio with RE 3+ ionic radius increases. High quality powder samples of LiCa RE 5 (BO 3) 6 (RE ​= ​Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y) were synthesized by high temperature solid state reactions. Rietveld refinements on all samples confirmed the co-occupancy of Ca2+ and RE 3+ at M1 and M3 sites, and LiCa(RE 0.95 Eu 0.05) 5 (BO 3) 6 (RE ​= ​Gd, Y, Lu) exhibits a bright red-orange emission. Image 1 • LiCa RE 5 (BO 3) 6 were synthesized by high temperature solid state reactions. • High quality powder XRD data confirm the phase purity. • Structure details were obtained by careful Rietveld refinements. • Ca2+ co-occupy with the rare earth cations at M1 and M3 sites. • LiCa(RE 0.95 Eu 0.05) 5 (BO 3) 6 (RE ​= ​Gd, Y, Lu) gives a bright red-orange emission. [ABSTRACT FROM AUTHOR]