Ba Site Research Articles

Insights into the Impact of Yttrium Doping at the Ba and Ti Sites of BaTiO3 on the Electronic Structures and Optical Properties: A First-Principles Study.

We reported a systematic study of the effects of Y doping BaTiO3 at Ba and Ti sites. We assessed the structural, electronic, and optical properties by employing first-principles calculations within the Tran–Blaha-modified Becke–Johnson (TB–mBJ) potential and generalized gradient approximation + U approaches. We calculated the lattice constants and bond lengths for pure and Y-doped BaTiO3. We explored the consequences of electronic structure and optical property modification because of Y doping in BaTiO3. Indeed, Y doping has led to various modifications in the electronic structures of BaTiO3 by inducing a shift of the conduction band through lower energies for the Ba site and higher energies for the Ti site. It was found that Y doping, either at Ba or at Ti sites, strongly enhanced the BaTiO3 dielectric constant properties. The transformation in bonding was explored via the charge density contours and Born effective charges. We used the state of art of polarization theory based on finite difference and Berry-phase approaches to investigate piezoelectricity. Y doping has increased the dielectric constants but canceled the piezoelectricity as they changed to metallic nature. We could look into the future for potential doping, preserving the semiconductor nature of BaTiO3 and increasing the permittivity with large dielectric loss.

Effect of Ba non-stoichiometry in Ba1-xZr0.1Ce0.7Y0.2O3-δ on its structure defect, sinterability and hydrogen permeability

Three powders of Ba0.95Zr0.1Ce0.7Y0.2O3-δ (BZCY095), BaZr0.1Ce0.7Y0.2O3-δ (BZCY), Ba1.05Zr0.1Ce0.7Y0.2O3-δ (BZCY105) with different Ba contents were synthesized using solid state reaction method. The effects of Ba non-stoichiometry on structure defect, sinterability and hydrogen permeability were investigated in details. The results of XRD and SEM revealed that the excess of BaO (BZCY105) was beneficial to the formation of single phase and membrane sinterability, while the deficiency of BaO (BZCY095) was counterproductive because of the vaporization of BaO at high temperature. Moreover, according to XPS, EPR, FT-IR, Raman and UV–Vis analysis, BZCY105 contained more oxygen vacancies than BZCY095 and BZCY. Additionally, the hydrogen permeation flux through BZCY105 membrane was the highest one because excess BaO favors protonic and grain boundary conductivities. Finally, the mechanism of Ba non-stoichiometry in Ba1-xZr0.1Ce0.7Y0.2O3-δ was proposed. For BZCY105, the excess BaO might be substituted into Ce site to form more oxygen vacancies. As for BZCY095, the dopant of Y might tend to be substituted into Ba site, decreasing the concentration of oxygen vacancy.

Tuning ferroelectricity by manipulating the global and local structure in a lead-free Sr-doped Ba(Ti1-x Snx)O3ceramics

The effect of 5% Sr substitution at the Ba site in Ba(Ti1-x Snx)O3 (BTSnx) system is investigated for , 0.075, and 0.12 compositions. The phase transition studies were carried out using dielectric, high-resolution X-ray diffraction, and PE hysteresis loop measurements. Rietveld refinements, along with dielectric studies on strontium-doped BTSnx reveal that the inter-ferroelectric phase boundaries observed in pure BaTiO3 approach the Tc line, with morphotropic phase boundary like behaviour. The PE hysteresis loops show enhanced polarization (≈ 190%) in Sr-doped BTSn5, which is attributed to the inter-ferroelectric phase instability (which facilitates polarization rotation, phase boundary motion, and domain wall motion), enhanced tetragonality (c/a), and increased unit-cell polarization evident from the amplitude of frozen phonon mode corresponding to the zone center of the cubic Brillouin zone. The ferroelectric polarization observed in the average-cubic-structure state of Sr-doped BTSn12 is attributed to the cooperative polar off-centre displacements of A (Ba2+/Sr2+) and B (Ti4+/Sn4+) site cations along and directions, respectively. Further, Sr-doped BTSn12 has high dielectric constant and low loss which makes this material an important composition for various technological applications.

Thermally Stable and Deep Red Luminescence of Sr1-xBax[Mg2Al2N4]:Eu2+ (x = 0-1) Phosphors for Solid State and Agricultural Lighting Applications.

The systematic substitution of Ba in the Sr site of Sr[Mg2Al2N4]:Eu2+ generates a deep-red-emitting phosphor with enhanced thermal luminescence properties. Gas pressure sintering (GPS) of all-nitride starting materials in Molybdenum (Mo) crucibles yields pure-phase red-orange-colored phosphors. Peaks in the synchrotron X-ray diffraction (SXRD) data show a systematic shift toward smaller angles due to the introduction of the larger Ba cation in the same crystal structure. The photoluminescence property reveals that Ba substitution shifts the original emission wavelength of Sr[Mg2Al2N4]:Eu2+ (625 nm) toward ∼690 nm for Ba[Mg2Al2N4]:Eu2+. Thermal stability measurement of Sr1-xBax[Mg2Al2N4] indicates a systematic increase in stability from x = 0 to x = 1. X-ray absorption near-edge spectroscopy (XANES) results demonstrate the coexistence of Eu2+ and Eu3+. The red-shift and the enhanced thermal stability reveals that the distance of the emitting 5d level to the conduction band of Ba[Mg2Al2N4]:Eu2+ is large. The ionic size mismatch of Eu occupying a Ba site reduces the symmetry, thereby further splitting the degenerate emitting 5d level and lowering the energy of the emitting center. The development of deep-red phosphors emitting at 670-690 nm (x = 0.8-1.0) offers possible candidates for plant lighting applications.

Electrochemical properties of Sr-doped layered perovskite as a promising anode material for direct hydrocarbon SOFCs

A direct utilization of hydrocarbon fuels in solid-oxide fuel cell (SOFC) has been considered a worthwhile and realizable goal. Admittedly, while great strides have been made toward this development goal, there still remain Ni-based anode materials issues to be resolved. In this regard, this study focuses on Sr effect on electrical and electrochemical behaviors in PrBaMn2O5+?? (PBM) to be employed as an anode in SOFC operation under hydrogen and hydrocarbon fuels. The electrical conductivity of A-site layered PrBa0.8Sr0.2Mn2O5+?? (PBSM) oxide reaches 3.74 S cm???1 at 800 ??C in H2, which is higher than that of PBM due to doping smaller Sr into Ba site and fully meets the requirement to be employed as an anode material. The electrochemical performance is evaluated using La0.9Sr0.1Ga0.8Mg0.2O3????? electrolyte-supported cell based on A-site layered PBSM anode with Co???Fe catalysts, and shows peak power density around 1.38 and 0.68 W cm???2 at 800 ??C in H2 and C3H8, respectively. Considering the electrical and electrochemical properties, A-site layered PBSM might offer the opportunities to discover and explore new high-performance anode material for direct hydrocarbon SOFCs.

Persistent luminescence excitation spectroscopy of BaAl2O4:Eu2+,Dy3+

BaAl2O4:Eu2+,Dy3+ is related, both by structure and luminescence, to one of the best persistent luminescent phosphors, SrAl2O4:Eu2+,Dy3+. At room temperature (RT), the green persistent emission of BaAl2O4:Eu2+,Dy3+ remains visible for hours after ceasing irradiation. Similar to SrAl2O4, BaAl2O4 with hexagonal P63 structure, has two M2+ sites, but, limited optical activity from the 2nd site is observed in the emission of BaAl2O4:Eu2+,Dy3+ - even at 77 K. Using combined approach of photoluminescence, thermoluminescence (TL), and persistent (excitation) luminescence measurements, the origin and properties of persistent luminescence of BaAl2O4:Eu2+,Dy3+ were studied in detail. Ultraviolet (UV) excited and persistent emission are identical and no contribution from the Eu2+ in the high-symmetry Ba site was observed. TL excitation spectra clarified the unstructured conventional excitation spectrum; now it is evident that defects or the Dy3+ co-dopant do not contribute to persistent luminescence via direct energy absorption. Mechanisms for persistent luminescence should thus be revised.

Yellow/Orange-Emitting ABZn2Ga2O7:Bi3+(A = Ca, Sr; B = Ba, Sr) Phosphors: Optical Temperature Sensing and White Light-Emitting Diode Applications

Recently, there has been growing interest in developing Bi3+-activated luminescence materials for optoelectronic applications. Herein, new yellow/orange-emitting ABZn2Ga2O7:Bi3+ (ABZGO, A = Ca, Sr; B = Ba, Sr) phosphors with tunable optical properties are synthesized by an alkaline earth cation substitution. When Sr2+ substitutes Ca2+ and Ba2+, the excitation wavelength has a red shift from 325 to 363 nm, matching well with the n-UV chip based white light-emitting diodes (WLEDs). CaBaZn2Ga2O7:0.01Bi3+ (CBZGO:0.01Bi3+) exhibits two evident emission peaks at 570 and 393 nm originating from the respective occupation of Ca and Ba sites by Bi3+ ions. The optical tuning of the CBZGO:Bi3+ phosphor is achieved by changing the Bi3+ doping content and excitation wavelength based on the selected site occupation. Differently, both SrBaZn2Ga2O7:0.01Bi3+ (SBZGO:0.01Bi3+) and Sr2Zn2Ga2O7:0.01Bi3+ (SZGO:0.01Bi3+) phosphors exhibit a single broad emission band, peaking at 600 and 577 nm, respectively. Two different Bi3+ sites are also verified respectively in SBZGO and SZGO hosts by the Gaussian fitting of the asymmetric PL spectra and lifetime analysis. The different luminescence behaviors of ABZGO:0.01Bi3+ phosphors should be ascribed to the synergistic effect of the centroid shift, crystal-field splitting, and Stokes shift. Moreover, the temperature-dependent PL spectra reveal that cation substitutions of Sr2+ for Ca2+ and Ba2+ can efficiently improve the thermal stability of ABZGO:0.01Bi3+ phosphors. In view of different thermal responses to various temperatures for two emission peaks of the CBZGO:0.01Bi3+ phosphor, an optical thermometer is designed and has a good relative sensitivity (Sr = 1.453% K–1) at 298 K. Finally, a WLED with CRI = 97.9 and CCT = 3932 K is obtained by combining SZGO:0.01Bi3+ and BAM:Eu2+ phosphors with a 370 nm n-UV chip, demonstrating that SZGO:0.01Bi3+ is an excellent yellow-orange-emitting phosphor for n-UV WLED devices. This work stimulates the exploration of optical tuning by cation substitution to obtain remarkable luminescence materials for optical temperature sensing and WLED applications.

A study of structural and dielectric properties of Ba2+ doped CH3NH3PbI3 crystals

An understanding of the effects of doping in lead perovskites may allow for improved solar cell performance or reduction in toxicity of the materials used. Ba2+ doped CH3NH3PbI3 (CH3NH3Pb1−xBaxI3 with x = 1%, 5% and 10%) are successfully synthesized by cooling down a concentrated aqueous solution containing HI, CH3NH2 and metal acetates and their properties are investigated using x-ray diffraction, differential scanning calorimetry, and impedance spectroscopy (IS). No new structures are formed upon doping with Ba2+ ions, however the lattice expands. The IS measurements show a strong increase in the conductivity and dielectric constants of the doped crystals. The conductivity arises mainly from vacancy mediated iodide ion (I−) migration and the increase in ionic conductivity with dopants is ascribed to increased defect formation due to lattice distortion. In addition, the bulk dielectric constant increases with increasing Ba2+ dopant. The increase in the dielectric constant is consistent with ordering of CH3NH3 dipoles resulting from distortions of the Ba sites in the lattice. The temperature dependence of the dielectric constants is attributed to thermal effects on the orientation of CH3NH3 molecules.

Stoichiometry control in molecular beam epitaxy of BaSnO3

La-doped $\mathrm{BaSn}{\mathrm{O}}_{3}$ films were grown on $\mathrm{DySc}{\mathrm{O}}_{3}$ substrates by molecular beam epitaxy using La, Ba, and $\mathrm{Sn}{\mathrm{O}}_{2}$ sources with and without additional oxidant, respectively. Lattice parameter measurements as a function of growth conditions show a reduced lattice parameter that is likely due to substitution of $\mathrm{S}{\mathrm{n}}^{2+}$ on the Ba site. The propensity for the antisite defect is discussed as being due to the combination of oxygen-poor, Sn-rich conditions and the dual valence of Sn. Although electron mobilities are highest for films with reduced lattice parameters, antisite defects will pose an upper limit to thin film mobility. Less Sn-rich conditions lead to the formation of another defect that causes a lattice expansion. The combined effects of these defects on the lattice parameter can compensate each other and cause the appearance of a stoichiometric lattice parameter for nonstoichiometric films with poor electrical behavior.

Morphological and structural properties of barium strontium titanate nanopowders synthesized via a sol-gel method

Barium strontium titanate (Ba1–xSrxTiO3, BSTO) powders were prepared using a sol-gel method. All of the samples were calcined at 800 °C. Effect of Sr concentration (x = 0, 0.3, 0.5, and 0.7) on morphological and structural properties of BSTO powders were investigated and discussed. Morphology of the BSTO powders revealed agglomerates of uniform irregular-shaped particles with sizes less than 100 nm. From X-ray analysis, all BSTO powders exhibited a cubic structure without any impurity or intermediate crystalline phases. The contraction of lattice constant and unit-cell volume of BSTO crystals was observed as the Sr concentration increased, confirming the incorporation of Sr into the Ba site. More detailed structural information of the BSTO powders was evaluated further through X-ray line profile analysis using the Williamson–Hall (W-H) plot. It was found that both the crystallite size and lattice strain of BSTO powders remained mostly unchanged with changing Sr concentration.

Cascade reaction engineering on zirconia-supported mesoporous MFI zeolites with tunable Lewis-Brønsted acid sites: a case of the one-pot conversion of furfural to γ-valerolactone.

Catalytic cascade reactions are strongly desired as a potential means of combining multistep reactions into a single catalytic reactor. Appropriate catalysts composed of multi-reactive sites to catalyze cascade reactions in a sequential fashion are central to such efforts. Here, we demonstrate a bifunctional zeolite catalyst with close proximity of Brønsted and Lewis acid sites through the synthesis of a mesoporous ZrO2[Al]MFI nanosponge (NS). The unique mesopores of the MFI-NS allow the confinement of zirconium oxide clusters (Lewis acid sites, LA) within the few-unit-cell-thin MFI aluminosilicate zeolite wall (Brønsted acid sites, BA). Such a structure is clearly distinct from the conventional MFI zeolite, where the agglomeration of zirconium oxide clusters onto the external surface area within the crystal bulk is not possible, resulting in segregated BA and LA sites on the internal and external zeolite, respectively. By bringing the BA and LA within ZrO2[Al]MFI-NS 30, we uncovered a more efficient catalytic route for the conversion of furfural (100% within 2 h) to γ-valerolactone (GVL) (83%). This route is only evident when the long molecular diffusion path, in the most extreme case of physically mixed ZrO2-(LA) and Al-zeolites (BA) (45% of GVL yield), is eliminated. Unlike the bifunctional ZrO2–Al-beta (GVL yield of 75%), where the BA concentration is greatly compromised at the expense of LA formation, we also show that the ZrO2[Al]MFI-NS is able to maintain a high density and good stability of both types of acids.

Structure and dielectric behavior of Cu-doped BaTiO3 ceramics

The influence of copper on the crystallographic phase and the microstructure of Ba1-xCuxTiO3 ceramics with the Cu2+ mole fraction, x, such as 0 ≤ x ≤ 0.30 was investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD analysis showed that Cu lowered the temperature of calcination of the pure sample, and that this dopant may occupy one or other of Ba and Ti sites. A gradual change from tetragonal to pseudo cubic structure was observed on doping with Cu. Dielectric measurements revealed that incorporation of Cu ions gave rise to appearance of diffuse character of the ferro-to-paraelectric transition together with weak relaxation and positive temperature coefficient of resistivity (PTCR) phenomena.

The stability of coordination polyhedrons and distribution of europium ions in Ca6BaP4O17.

In this work, the coordination polyhedron stabilities and distributions of europium ions in Ca6BaP4O17 (CBPO) luminescent materials are investigated. The density functional theory (DFT)-based first principles calculation results show that the PO4 tetrahedrons can tilt in the structure, which leads to the atomic distortion of O13 and O12 in CBPO and the Eu2+/Eu3+-doped systems. The energy scale of about ∼0.1 eV suggests that stabilities of coordination polyhedrons are easily influenced by dynamic factors. The atomic distortion and vacancy of work as charge compensations in CBPO:Eu3+, and three lattice sites of europium are extracted and summarized. The X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) confirm that Eu3+ can occupy the Ca1, Ca2 and Ba sites of CBPO. The combination of first principles calculation and X-ray absorption fine structure (XAFS) provides more information about microstructures of luminescent materials.

Effect of Sr substitution on electrical polarization of Ba1-xSrxTiO3 (x = 0.0, 0.2, 0.6, and 0.8) perovskite materials

This study aims to investigate the electrical polarization of Ba1-xSrxTiO3 (x = 0.0, 0.2, 0.6, and 0.8) perovskite materials. The materials were synthesized using mechano-synthesis. The structural behaviour was assessed using X-ray diffractometer (XRD), revealing that all samples have a tetragonal perovskite structure with a lattice parameter that decreases with an increase in Sr. The electrical polarization was investigated using an electrometer, showing decreasing spontaneous and saturation polarizations as more Sr is substituted into the Ba sites of (Ba,Sr)TiO3. The decreasing lattice parameters and spontaneous and saturation polarizations in these materials indicate that the crystal structure changes from tetragonal to cubic as more Sr is added.

Magnetism and transport in transparent high-mobility BaSnO3 films doped with La, Pr, Nd, and Gd

We have explored the effect of magnetic rare-earth dopants substitutionally incorporated on the Ba sites of ${\mathrm{BaSnO}}_{3}$ in terms of electronic transport, magnetism, and optical properties. We show that for ${\mathrm{Ba}}_{0.92}{R}_{0.08}{\mathrm{SnO}}_{3}$ thin films (where $R=\text{La,}\phantom{\rule{4.pt}{0ex}}\text{Pr,}\phantom{\rule{4.pt}{0ex}}\text{Nd,}\phantom{\rule{4.pt}{0ex}}\text{Gd}$), there is a linear increase of mobility with carrier concentration across all doping schemes. La-doped films have the highest mobilities, followed by Pr- and Nd-doped films. Gd-doped samples have the largest ionic size mismatch with the Ba site and correspondingly the lowest carrier concentrations and electron mobilities. However, crystallinity does not appear to be a strong predictor of transport phenomena; our results suggest that point defects more than grain boundaries are key ingredients in tuning the conduction of ${\mathrm{BaSnO}}_{3}$ films grown by pulsed laser deposition. Pronounced, nonhysteretic x-ray magnetic dichroism signals are observed for Pr-, Nd-, and Gd-doped samples, indicating paramagnetism. Finally, we probe the optical constants for each of the ${\mathrm{BaSnO}}_{3}$ doping schemes and note that there is little change in the transmittance across all samples. Together these results shed light on conduction mechanisms in ${\mathrm{BaSnO}}_{3}$ doped with rare-earth cations.

Effect of La-doping on dielectric properties and energy storage density of lead-free Ba(Ti[formula omitted]Sn[formula omitted])O[formula omitted] ceramics

Lead-free Ba1–zLazTi0.95Sn0.05O3 with z=0.00, 0.015, 0.025, and 0.035 samples were prepared using solid-state reaction route. X-ray diffraction measurement reveals the single phase formation of ceramic samples. Scanning electron microscopy shows the inhibited grain growth (≤0.5 μm) at low La-doping while the higher La-doping in BTS ceramics yielded the larger grain size (2.5 μm). Raman spectra indicate the substitution of La at Ba site sublattice. Dielectric properties improved with La-doping in BTS ceramic samples. 3.5LBTS sample exhibits energy storage density as high as (Jd) ∼ 0.492 J/cm3 with an energy efficiency of 63% at ∼40 kV/cm, which is 5.5 times more than that of pure BTS ceramics. Such significant increment in energy storage density could be attributed to reduced grain size due to La-doping. Thus, the selected composition could be a new method for enhancing the energy storage density for device applications.

Site occupancy and tunable photoluminescence properties of Eu2+-Activated Ba3Sc(BO3)3 phosphors for white light emitting diodes

A series of emission-tunable Ba3-xSc(BO3)3: xEu2+ (0 ≤ x ≤ 0.15) and Ba2.97-yGdySc1-yMgy(BO3)3: 0.03Eu2+ (0 ≤ y ≤ 0.15) phosphors were synthesized by a solid-state method. Structure analysis of X-ray powder diffraction (XRD) and Rietveld refinement show that Eu2+ ions occupy randomly at Ba sites of hexagonal lattice with space group P63cm. Photoluminescence emission spectra and the decay curves of phosphors demonstrated the existence of multiple Eu2+ emitting centers. Eu2+ ions occupy at four Ba sites of Ba3-xSc(BO3)3: xEu2+ (0.03 ≤ x ≤ 0.15) emit orange light (λem = 670 nm and 560 nm) through 370 nm UV excitation. The broader absorption band, ranging from 220 nm to 550 nm, matches well with the near-ultraviolet LED chips. Furthermore, color tuning from orange to red is successfully achieve by the double doping of Gd3+-Ba2+ and Mg2+-Sc3+ in Ba2.97Sc(BO3)3: 0.03Eu2+. Our results indicate that red emission Ba3Sc(BO3)3: Eu2+ phosphors is an ideal candidate for the application in white light-emitting diodes.

Structural and optical properties of Ba3(Nb6−xTax)Si4O26 (x = 0.6, 1.8, 3.0, 4.2, 5.4)

Structure and optical properties have been successfully determined for a series of niobium- and tantalum-containing layered alkaline-earth silicate compounds, Ba3(Nb6−xTax)Si4O26 (x = 0.6, 1.8, 3.0, 4.2, 5.4). The structure of this solid solution was found to be hexagonal P-62m (No. 189), with Z = 1. With x increases from 0.6 to 5.4, the lattice parameter a increases from 8.98804(8) to 9.00565(9) Å and c decreases from 7.83721(10) to 7.75212(12) Å. As a result, the volume decreases from 548.304(11) to 544.479(14) Å3. The (Nb/Ta)O6 distorted octahedra form continuous chains along the c-axis. These (Nb/Ta)O6 chains are in turn linked with the Si2O7 groups to form distorted pentagonal channels in which Ba ions were found. These Ba2+ ions have full occupancy and a 13-fold coordination environment with neighboring oxygen sites. Another salient feature of the structure is the linear Si–O–Si chains. When x in Ba3(Nb6−xTax)Si4O26 increases, the bond valence sum (BVS) values of the Ba sites increase slightly (2.09–2.20), indicating the size of the cage becoming progressively smaller (over-bonding). While SiO cages are also slightly smaller than ideal (BVS range from 4.16 to 4.19), the (Nb/Ta)O6 octahedral cages are slightly larger than ideal (BVS range from 4.87 to 4.90), giving rise to an under-bonding situation. The bandgaps of the solid solution members were measured between 3.39 and 3.59 eV, and the x = 3.0 member was modeled by density functional theory techniques to be 3.07 eV. The bandgaps of these materials indicate that they are potential candidates for ultraviolet photocatalyst.

Synthesis and Photoluminescence Properties of Novel BaSi4O6N2:Eu2+ Phosphor for White- LEDs

Presently commercial white-LEDs employ a blue LED chip and a yellow light-emitting phosphor, and are very poor in the color rendering index (CRI) [1]. Therefore, novel blue, green and red phosphors showing broad emission spectra have studied recently. BaSi4O6N2 has been recently reported to have a structure similar to Ba3Si6O12N2 green phosphor which shows not sharp but not broad emission [2-3]. To the best of our knowledge, there is no report that succeeded in synthesizing pure BaSi4O6N2 crystal phase, and no report that the materials related to BaSi4O6N2 shows fluorescence in visible region. In this study, we investigated optimum sintering conditions and composition to obtain pure BaSi4O6N2 crystal phase by solid state reaction technique. We also examined the optical property of Eu2+ activated BaSi4O6N2 as well as the crystal structure through X-ray Rietveld refinement. Although we optimized sintering temperature and duration (1100 °C and 2 h) to obtain exclusively BaSi4O6N2 crystal phase, impurity phases such as Ba3Si6O12N2 still remained. Therefore, we tried to suppress the formation of Ba3Si6O12N2 phase by adding Si3N4 raw material in excess of stoichiometric ratio of BaSi4O6N2 (Si/Ba = 4-6). As shown in Fig. 1, by increasing the Si/Ba ratio to be more than 4, the peaks which derived from Ba3Si6O12N2 and oxides (SiO2, Ba2Si4O10) decreased in intensity. No other impurity phases were observed in the XRD pattern of the sample with Si/Ba = 6. However, SEM-EDS analysis supported that the monophasic sample possessed the stoichiometric composition as BaSi4O6N2.The lattice parameters of BaSi4O6N2 which crystallized in a hexagonal unit cell were a = 5.2573 (16) and c = 7.7295 (59)Å in the sample with Si/Ba = 6. Compared to the reported lattice parameters a = 5.351 and, c = 7.523Å of BaSi4O6N2 (JCPDS 82-4088), the a length was longer and the c length was shorter. As shown in Fig. 2, X-Ray Rietveld analysis of our BaSi4O6N2 demonstrated that the difference in the lattice parameters would come from the different occupation probability of two distinct Ba sites in the structure [4]. One is called the Ba1 site whose coordination number by anion is 12 and the other is 6-fold Ba2 site. The previous paper reported that Ba species were distributed to these sites with occupation probabilities of Ba1:Ba2 = 87:13 [3]. However, our oxynitride possessed neither Ba nor Eu at the Ba1 site. As shown in Fig. 3, broad spectra with the emission peak of around 405 nm were observed under the excited light of 320 nm. This emission is ascribed to the 4f65d1→4f7 transition of Eu2+. In addition, the emission spectrum of BaSi4O6N2:Eu2+ possesses FWHM about 185 nm. It was obviously broader band compared with that of Ba3Si6O12N2:Eu2+ emission with FWHM about 70 nm. It indicates that this phosphor is fascinating for high CRI white-LEDs.

Destruction of multiferroicity in Tb2BaNiO5 by Sr-doping and its implication to magnetodielectric coupling

The Haldane spin-chain compound, Tb2BaNiO5, with two antiferromagnetic transitions, one at T1 = 63 K and the other at T2 = 25 K, has been recently shown to be an exotic multiferroic below T2. Here, we report the results of our investigation of Sr doping at the Ba site by magnetization, heat-capacity, magnetodielectric (MDE) and pyrocurrent measurements. An intriguing finding, which we stress, is that the ferroelectricity is lost even for a doping level of ten atomic percent, though magnetic ordering prevails. The doped specimens however retain significant MDE behaviour, but with reduced magnitudes and qualitative changes with respect to the behaviour of the parent compound. This implies that ferroelectric order is also crucial for the anomalously large MDE in the parent compound, in addition to the role of 4f single-ion anisotropy.