Ba Substitution Research Articles

Preparation and characterization of Ba-substituted Li1+xAlxGe2−x(PO4)3 (x = 0.5) solid electrolyte

Abstract The substitution of Al in LAGP (Li 1+x Al x Ge 2−x (PO 4 ) 3 ) by a divalent cation of Ba has been investigated in this study. The Ba-substituted glassy LAGP is prepared by a melt-quenching method, followed by crystallization from 750 to 850 °C for 8 h. The thermal gravity and differential thermal analysis (TG-DTA) and high temperature X-ray diffraction (HT-XRD) measurements reveal that the Ba substitution reduces the temperature of the onset of crystallization. The influence of the crystallization temperature on crystallinity, morphology and Li ion conductivity of LAGP is also studied. The formation of an impurity such as AlPO 4 and BaGeP 2 O 8 is observed in all samples and is promoted by an increase in the crystallization temperature. The Li ion conductivities of the Ba-substituted LAGP (LABGP) crystallized at 750, 800 and 850 °C are 4.7 × 10 −4 , 2.9 × 10 −4 , and 1.9 × 10 −4 S cm −1 , respectively. The LABGP crystallized at 750 °C contains more mobile Type II Li ions than others indicated by X-ray photoelectron spectroscopy (XPS), which contribute to improve the bulk Li ion conductivity, and as observed in the scanning electron microscope (SEM) image, it also contains more of the amorphous component, which reduces the grain-boundary resistance. As a result, the LABGP crystallized at 750 °C shows the highest Li ion conductivity. By suppressing the impurity formation, further improvements in the Li ion conductivity can be expected.

Dielectric properties of crystals of (Pb1–x Ba x )5Ge3O11 solid solutions

Crystals of (Pb1–x Ba x )5Ge3O11 (0 ≤ x < 0.12) ferroelectric solid solutions have been grown via slow melt cooling and characterized by X-ray diffraction and dielectric measurements. The results demonstrate that the partial Ba substitution for Pb atoms in the crystals leads to a monotonic increase in their hexagonal cell parameters and a rather drastic degradation of their ferroelectric properties: a decrease in their Curie temperature T C from 450 to 120 K and a decrease and broadening of the peaks in their dielectric permittivity emax and dielectric loss tangent tan δmax at T C. In addition to the dielectric anomalies near T C, the dielectric properties of the crystals demonstrate features of relaxation character in the ranges 220–260 and 20–170 K. Starting in the composition range x = 0.06–0.08, emax increases with Ba content, instead of decreasing. Moreover, in this composition range the dielectric properties of the crystals depend markedly on their thermal history. The observed anomalies in the temperature and composition dependences of the dielectric properties of the solid solutions have been interpreted in terms of the dynamics of the thermal localization of charge carriers at defect levels with ionization energies Ua1 ≈ 0.6 eV and Ua2 ≈ 0.2 eV, as well as at shallower levels, in the temperature range 240–280 K and below 160 K, respectively, and the shift of T C to these temperature ranges with increasing Ba content.

Magnetic properties of exchange-enhanced Pauli paramagnetic metals AeCo2P2 (Ae = Sr, Ba)

We have synthesized single crystals of AeCo2P2 (Ae = Sr, Ba) and polycrystalline powder sample of Sr1−xBaxCo2P2, and measured their magnetic properties. SrCo2P2 shows an itinerant-electron metamagnetic transition at Hc = 600 kOe and its temperature dependent magnetic susceptibility shows characteristic two anomalies at Tmax1 = 25 and Tmax2 = 115 K, suggesting it is in the vicinity of a ferromagnetic quantum critical point. While, BaCo2P2 does not show the metamagnetic transition with the applied field up to 600 kOe, and its magnetic susceptibility shows only one anomaly corresponding to Tmax1 at 33 K. In addition, the Weiss temperature of Sr1−xBaxCo2P2, decreases to negative as x increases. These results indicate the system recede from the quantum critical point by the Ba substitution.

Synthesis and Study of the Effect of Ba2+ Cations Substitution with Sr2+ Cations on Structural and Optical Properties of Ba2-xSrxZnWO₆ Double Perovskite Oxides (x = 0.00, 0.25, 0.50, 0.75, 1.00).

The effect of Sr2+ substitution on the morphology, crystal structure, and optical properties of double perovskite oxide Ba2−xSrxZnWO6 (x = 0.00, 0.25, 0.50, 0.75, 1.00) were investigated. Scanning electronic microscopy demonstrated that all samples have similar microstructure morphology but differ in the range of grain sizes. X-ray diffraction measurements indicated that these materials crystallize in a (Fm-3m) cubic crystal structure, and also confirmed the tolerance factor. Rietveld analysis revealed that the lattice parameter decreased from 8.11834 to 8.039361 Å when the substitution of Ba2+ with Sr2+ cations increased from zero to 100%. Fourier transform infrared (FTIR) and Raman spectroscopies displayed a symmetric stretching vibration of WO6 octahedra at 825 cm−1, and an anti-symmetric stretching mode of WO6 was observed by FTIR at 620 cm−1. A strong peak at 420 cm−1 was also observed in the Raman spectra and is due to the W–O–W bending vibration modes. UV-Vis diffuse reflectance spectroscopy was carried out for the series, and the band gap energy decreased from 3.27 eV for Ba2ZnWO6 to 3.02 and 3.06 eV for Ba1.75Sr0.25ZnWO6 and Ba1.5Sr0.5ZnWO6, respectively. The excitation and emission photoluminescence properties were investigated at room temperature.

Structural investigation of the SrAl2O4-BaAl2O4 solid solution system with unstable domain walls

We investigated the structural phase transition of the Ba1−xSrxAl2O4 solid-solution system (x⩾0.6) via in situ powder X-ray diffraction and transmission electron microscopy. The sequence of structural phase transitions P6322↔P63(3ap)↔P21 occurs in a composition window of x=0.8–1.0. Ba substitution suppresses the P63 intermediate and low-temperature P21 phases, which disappear at x=0.7 and 0.6, respectively. The P21 phase boundary exhibits first-order characteristics, at which the cell parameters change discontinuously and the cell volume slightly contracts as the temperature increases. In the P21 phase, unstable twin walls are observed; the shapes and the crystal axes of each twin domain change as the temperature increases. This instability can be attributed to the latent instabilities that both the BaAl2O4 and SrAl2O4 compounds possess.

Comparison of benzene and toluene photodegradation under visible light irradiation by Ba-doped BiFeO3 magnetic nanoparticles with fast sonochemical synthesis.

Bi1-xBaxFeO3 (x = 0.02, 0.04 and 0.07) multiferroic materials with a diameter in the range of 30-40 nm were controllably synthesized by a facile ultrasonic method, with a very short reaction time of 5 min at a low temperature of 30 °C, and the resulting BiFeO3 magnetic nanoparticles (BFO MNPs) exhibited enhanced magnetic and photocatalytic performance. The substitution of Ba2+ ions for Bi3+ ions at the A-site of BFO MNPs, even at only 2%, decreased their particle size and distorted the lattice in the rhombohedral structure of BFO MNPs. Increasing the Ba doping to 7% greatly increased the ferromagnetic properties of BFO MNPs from 3.55 to 6.09 emu g-1. In comparison with pure BFO MNPs, 7% Ba substitution in the Ba-doped BFO MNP samples produced strong absorption in the visible light region, decreasing the band-gap energy from 2.11 to 1.86 eV. Photoluminescence (PL) spectroscopy identified the band-gap emission for BFO MNPs at 587 nm, while for both pure and Ba-doped samples, the other emissions were attributed to the defect states related to oxygen deficiencies inside the band gap. After 50 min of visible light irradiation, Bi1-xBaxFeO3 (x = 7%), with the lowest band gap energy, highest magnetization and smallest particle size, showed almost complete photocatalytic degradation of toluene and benzene (100 mg L-1), with 91 and 81% reduction, respectively, in total organic carbon (TOC). For all irradiation times, the mineralization efficiency of toluene was higher than that of benzene, which demonstrated that toluene is more sensitive to photocatalytic oxidation than is benzene.

Crystal Structure and Oxide-Ion Conductivity of Ba1+xNd1−xInO4−x/2

BaNdInO4 is a new structure family of oxide-ion conductors. In the present work, we have investigated the crystal structure and electrical conductivity of Ba1+xNd1−xInO4−x/2 where x is the excess Ba content. It was found that Ba1.1Nd0.9InO3.95 shows (i) about 12 times higher oxide-ion conductivity at 858°C and (ii) a little lower activation energy for oxide-ion conduction than BaNdInO4. The higher oxide-ion conductivity of Ba1.1Nd0.9InO3.95 is mainly ascribed to higher carrier concentration. Careful structure analyses using both the single-crystal X-ray diffraction and time-of-flight (TOF) neutron powder diffraction data enabled to determine the position of excess Ba cation and occupancy factor of O anion. It was found that the excess Ba cation substitutes for Nd cation and that oxygen vacancies exist in Ba1.1Nd0.9InO3.95. The refined occupancy factor of oxygen atom 0.9829(17) indicates the higher concentration of oxygen vacancies in Ba1.1Nd0.9InO3.95, compared with BaNdInO4, giving higher oxide-ion conductivity in Ba1.1Nd0.9InO3.95. The larger-sized Ba substitution for Nd cation makes the bottleneck size larger, leading to the lower activation energy. The bond valence-based energy landscape calculated for the refined crystal structure of Ba1.1Nd0.9InO3.95 at 800 and 24°C indicated two-dimensional oxide-ion diffusion in the A rare earth oxide (Nd,Ba)2O3 unit on the bc plane.

Impact of Ba Substitution on the Magnetocaloric Effect in La1-xBaxMnO3 Manganites

La1-xBaxMnO3 (x = 0.30, 0.35 and 0.40) samples have been prepared by solid-state reaction method. The X-ray diffraction (XRD) study showed that all the samples crystallized in a rhombohedral structure with an R-3c space group. Variation of the magnetization as a function of the temperature and applied magnetic field was carried out. All the samples revealed ferromagnetic to paramagnetic (FM-PM) phase transition at the Curie temperature TC ~ 342 K. The magnetic entropy change was also studied through examination of the measured magnetic isotherms M(H, T) near TC. The magnetocaloric effect was calculated in terms of the isothermal magnetic entropy change. The maximum entropy change reaches a value of 1.192 J/ kgK under a magnetic field change of 2.5T for the La0.6Ba0.4MnO3 composition. The relative cooling power (RCP) is 79.31 J/ kg for the same applied magnetic field.

Structural and multiferroic properties of barium substituted bismuth ferrite nanocrystallites prepared by sol–gel method

Nanocrystalline Bi1-xBaxFeO3 (0≤x≤0.3) multiferroics were efficiently obtained by sol–gel method after sintering at 800°C for one hour. The Ba substitution in BiFeO3 (BFO) strongly modifies its structural and multiferroic properties. XRD studies revealed the structural transition from distorted rhombohedral (R3c) to pseudo-cubic (Pm3m) crystal symmetry. The magnetization increases appreciably for x=0.1, which is due to spin canting of magnetic moments at the nanoparticle surfaces and decreases afterward. From the temperature dependent magnetization studies, it is found that magnetic transition temperature (TN) is 620K for x=0 and 640K for x=0.1. Besides, the maximum polarisation value decreases with increasing Ba content. SEM micrographs revealed the formation of cubic nanocrystallites with increased porosity on Ba substitution. FTIR analysis of the samples also supports the structural change towards increased crystal symmetry.

Magnetization, phonon, and X-ray edge absorption in barium-doped BiFeO3 ceramics

Magnetization hysteresis loops, dc and ac magnetic susceptibilities, and Raman vibrations have been characterized in (Bi1−x Ba x )FeO3−δ ceramics for x = 0.0, 0.05, 0.10, and 0.15 as functions of temperature. Ferromagnetic hysteresis loops were observed in Ba-doped compounds with increasing magnetization as Ba substitution increases. High-resolution synchrotron Fe K- and L 2,3-edge X-ray absorptions reveal an Fe3+ valence and a modification of the Fe–O–Fe bond structure by the A-site Ba substitution. The oxygen K-edge X-ray absorption suggests that the hybridization of the O 2p and Fe 3d orbitals was reduced by the Ba2+ substitution. Field-cooled and zero-field-cooled magnetic susceptibilities reveal a spin-glass behavior, which was enhanced with increasing Ba substitution. Raman vibrations of the Bi- and Fe-sensitive E(2) and A 1(1) modes reveal frequency softening and step-like anomalies in full-width-at-half-maximum in the vicinity of ~150–250 K, which were attributed to spin–phonon interaction while magnetic ordering transitions take place.

(Invited) Steam Electrolysis Using Proton-Conducting Perovskite

Water electrolysis is an important technology for producing renewable hydrogen and work for energy conversion between the electricity and hydrogen in combination with hydrogen fuel cells. Steam electrolysis is characterized by low electrolysis voltage in comparison with other methods. Proton conduction in alkali earth cerates, zirconates and their solid solutions is useful for steam electrolysis, as well as hydrogen fuel cells, since it is less temperature-dependent than oxide ion conduction in zirconia and ceria based electrolytes. This aspect enables us to operate steam electrolysis at intermediate temperatures and hence to reduce the cost for production and operation. In addition, as schematically illustrated in Fig. 1, steam electrolysis using proton conducting electrolyte requires steam in the anode compartment, being a benefit of proton conductor cells because hydrogen generated at the cathode will already be separated from steam.This paper demonstrates conductivity and stability of some perovskite-type proton conducting metal oxides and the intermediate temperature operation of steam electrolysis. We also discusses several challenges of the proton conductor cells particularly for the electrolysis mode of operationWhen SrZr0.5Ce0.4Y0.1O3-δ (denoted below as SZCY541) is used as the electrolyte for the steam electrolysis, electrolysis voltage as low as 1.2 V has been attained for the current density of 0.1 A/cm2at 600°C, using 1% hydrogen and 1% oxygen as the cathode and anode gases, respectively. The voltage is equivalent to 1.4 V for air/pure hydrogen gas atmospheres, corresponding to around 90% of energy efficiency (HHV; vaporization of water considered for required energy).Starting from SZCY541 used in the above mentioned experiment, we examined the effects of Ba substitution for Sr and the doping level of Y on the lattice structure, electrical properties, proton content as well as chemical stability. In the examination keeping the ratio of Zr/Ce to be 5/4, Ba(Zr5/9Ce4/9)0.8Y0.2O3-δ, BZCY(54)8/92, has been found to show high proton conductivity: proton conductivity of 1.44 × 10-2 Scm-1 in wet 1 % H2 at 600°C. By use of this electrolyte, higher steam electrolysis performance can be obtained compared to the SZCY541 case shown above.There are still several challenges for the proton conductor cell to be applied for steam electrolysis. One is the stability of anode in steam. Several transition metal containing perovskites, such as Sm0.5Sr0.5CoO3 (SSC55) can be used as the anode with acceptable electrode performance, but these materials are not sufficiently durable against high steam concentration at intermediate temperature, e.g. 600°C, and SSC55 anode time dependently deteriorates. Another issue is the inter-diffusion of transition metal species from the electrodes to the electrolyte causing the reduction of the proton conductivity. We have examined the impact of several transition metals by introducing them as a part of the B-site component of AB 0.9Y0.1O3-δ (A=Ba, Sr; B=Ce, Zr) to find the proton conductivity is more or less reduced by the transition metal incorporation. Electronic leakage is another crucial problem of the proton conductor steam electrolysis, i.e., electrolysis rates deviates lower from that based on Faraday’s low of electrolysis. This is due to a partial electronic current flow originated from electron hole staying in the perovskite in oxidative atmosphere, anode environment in the electrolysis case, and penetrating the cathode on applying high current density. These challenges as well as possible solutions for some will be explained in this talk. AcknowledgementThis work was supported by the Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), "energy carrier" (Funding agency: JST) and by World Premium International Research Center Initiative (WPI), MEXT Japan. Figure 1

Proton Conduction Properties of Bzcy and Szcy Perovskites Type Oxides; Addressing the Effect of Dopant Levels and Proton Content

Electrochemical devices based on perovskites-type proton conducting oxides, are gaining wide interest as promising green technologies for hydrogen production and seperation. Interest in this class of materials stems from their lower activation energy for proton transport (typically 0.3-0.6 eV) relative to that for oxide ion conduction, thus making them suitable electrolyes for steam electrolysis cell operation at intermediate temperature. Despite the advances in proton-conducting electrolytes, their development still lag behind the oxygen-ion counterparts. The most prominent limitation being, conductivity, chemical stability, incomplete hydration of the electrolytes, as well as the grain boundary resistance. In the present contribution, starting from SrZr0.5Ce0.4Y0.1O3-δ, we examined the effects of Ba substitution for Sr and the doping level of Y on the lattice structure, electrical properties, proton content as well as chemical stability of the following compositions A(Zr5/9Ce4/9)1-x Y x O3- δ , (A= Ba, Sr and x=0.1, 0.2). Thermo-gravimetric analyses revealed almost similar proton concentration in both SZCY541 and SZCY(54)8/9-2 with a constant Zr/Ce fraction of 5:4. Both samples showed almost comparable proton conductivities in humidified 1% H2 hydrogen. BZCY(54)8/9-2 shows a maximum proton limit of 13.3 mol % compared to only 6.03 mol % for SZCY(54)8/9-2 and retained the highest proton conductivity of 1.44 × 10-2 Scm-1 in wet 1 % H2 at 600 oC (Fig. 1.) as well as excellent chemical stability under 80 % steam for 200 hours. Ba at A-site provides higher proton mobility than Sr. It is also evident from the data that the bulk and grain boundary contributions on the conductivity were strongly dependent on the A-site host, with the grain boundary response dominating the impedance spectra of the BZCY system relative to the SZCY. However the major difference in conductivity among the compositions originates mostly from the differences in proton concentration levels as well as the magnitude of the grain boundary contribution. This paper discusses these aspects based on experimental results as well as steam electrolysis using SZCY541 and BZCY(54)8/9-2 as electrolytes. Acknowledgement This work was supported by the Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), “energy carrier”(Funding agency: JST) and by World Premium International Research Center Initiative (WPI), MEXT Japan. Figure 1

High-temperature complex impedance and modulus spectroscopic studies of doped Na0.5Bi0.5TiO3-BaTiO3 ferroelectric ceramics

Lead-free Na0.5Bi0.5TiO3 (NBT) and (1 − x)Na0.5Bi0.5TiO3 + xBaTiO3 with x = 0.1 and 0.2 (where x = 0.1 and 0.2 are named as NBT1 and NBT2, respectively), (1 − y)Na0.5Bi0.5TiO3 + yBa0.925Nd0.05TiO3 with y = 0.1 and 0.2 (where y = 0.1 and 0.2 are named as NBT3 and NBT4, respectively)-based relaxor ferroelectric ceramics were prepared using the sol-gel method. The crystal structure was investigated by X-ray diffraction (XRD) at room temperature (RT). The XRD patterns confirmed the presence of the rhombohedral phase in all the samples. The electrical properties of the present NBT-based samples were investigated by complex impedance and the modulus spectroscopy technique in the temperature range of RT–600 °C. The AC conductivity was found to increase with the substitution of Ba2+ ions to the NBT sample whereas it significantly decreased with the addition of Nd3+ ions. The more anion vacancies in Ba-added samples and the lower anion vacancies in Nd-added samples were found to be responsible for higher and lower conductivities, respectively.

Effect of Ba Substitution on Dielectric and Piezoelectric Properties of Lead-Free Bi1/2(Na0.82K0.18)1/2TiO3 Ceramics

Effect of Ba Substitution on Dielectric and Piezoelectric Properties of Lead-Free Bi_1/2(Na_0.82K_0.18)_1/2TiO₃ Ceramics

Development of Lithium-Stuffed Garnet-Type Oxide Solid Electrolytes with High Ionic Conductivity for Application to All-Solid-State Batteries

All-solid-state lithium-ion battery (LiB) is expected as one of the next generation energy storage devices because of their high energy density, high safety and excellent cycle stability. Although oxide-based solid electrolyte materials have rather lower conductivity and poor deformability than sulfide-based one, they have other advantages such as their chemical stability and easiness for handling. Among the various oxide-based SEs, lithium stuffed garnet-type oxide with the formula of Li7La3Zr2O12 (LLZ) have been widely studied because of their high conductivity above 10-4 Scm-1 at room temperature, excellent thermal performance and stability against Li metal anode.Here, we present our recent progress for the development of garnet-type solid electrolytes with high conductivity by simultaneous substitution of Ta5+ into Zr4+ site and Ba2+ into La3+ site in LLZ. Li+ concentration was fixed to 6.5 per chemical formulae, so that the formulae of our Li garnet-type oxide is expressed as Li6.5La3-xBaxZr1.5-xTa0.5+xO12 (LLBZT) and Ba contents x are changed from 0 to 0.3. As results, all LLBZT samples have cubic garnet structure without containing any secondary phases. The lattice parameters of LLBZT decrease with increasing Ba2+ contents x < 0.10 while increase with x from 0.10 to 0.30, possibly due to the simultaneous change of Ba2+ and Ta5+ substitution levels. Relative densities of LLBZT are in the range between 89% and 93% and not influenced so much by the compositions. From AC impedance spectroscopy measurements, the total (bulk + grain) conductivity at 27oC of LLBZT shows its maximum value of 8.34 x 10-4 S cm-1 at x = 0.10, which is slightly higher than the conductivity (= 7.94 x 10-4 S cm-1) of LLZT without substituting Ba (x = 0). Activation energy of the conductivity tends to become lower by Ba substation, while excess Ba substitution degrades the conductivity in LLBZT. LLBZT has wide electrochemical potential window of 0-6 V vs. Li+/Li and reversible Li+ insertion and extraction reactions of TiNb2O7 film electrode formed on LLBZT by aerosol deposition are successfully demonstrated at 60oC. The results indicate that LLBZT can potentially be used as a solid electrolyte in all-solid-state batteries.

Incorporation of Ba in Al and Fe pollucite

Ba, the transmutation product of radioactive Cs, can be incorporated at levels of up to ∼0.07 formula units in Cs(1−2x)BaxAlSi2O6 aluminium pollucite formed by sol-gel methods and sintering at 1400 °C, with more Ba forming BaAl2Si2O8 phases. The effect of Ba substitution in pollucite-structured CsFeSi2O6 was also studied and no evidence of Ba substitution in the pollucite structure via cation vacancies or Fe2+ formation was obtained. The Ba entered a Fe-silicate glass structure. Charge compensation was also attempted with a Cs+ + Fe3+ ↔ Ba2+ + Ni2+ scheme but again the Ba formed a glass and NiO was evident. PCT leaching data showed CsFeSi2O6 to be very leach resistant.

Synthesis and Characterization of Ba and Ta Substituted Garnet-Type Li7La3Zr2O12 Solid Electrolyte for All-Solid-State Lithium Battery

All-solid-state lithium-ion battery (LiB) is expected as one of the next generation energy storage devices because of their high energy density, high safety and excellent cycle stability. Although oxide-based solid electrolyte materials have rather lower conductivity and poor deformability than sulfide-based one, they have other advantages such as their chemical stability and easiness for handling. Among the various oxide-based solid electrolytes, cubic garnet-type oxide with the formula of Li7La3Zr2O12 (LLZ) have been widely studied because of their high conductivity above 10-4 Scm-1 at room temperature, excellent thermal performance and stability against Li metal anode. Li7La3Zr2O12 (LLZ) have been widely studied because of their high conductivity above 10-4 Scm-1 at room temperature, excellent thermal performance and stability against Li metal anode. LLZ has two different crystal phases, one is cubic phase and another is tetragonal one, but high conductivity above 10-4 Scm-1 at room temperature is mostly confirmed in cubic phase sintered at high temperature. The concentration of Li+ in a garnet framework has crucial importance to stabilize cubic phaseIn this study, we present our recent progress for the development of garnet-type solid electrolytes with high conductivity by simultaneous substitution of Ta5+ into Zr4+ site and Ba2+ into La3+ site in LLZ. Li+ concentration was fixed to 6.5 per chemical formulae, so that the formulae of our Li garnet-type oxide is expressed as Li6.5La3-xBaxZr1.5-xTa0.5+xO12 (LLBZT) and Ba contents x are changed from 0 to 0.3. We don’t use Al2O3 crucible for sample synthesis because Al3+ contamination from the crucible into the LLBZT lattice during high temperature sintering may influence on Li+ concentration and the contamination level is very difficult to control. As results, all LLBZT samples have cubic garnet structure without containing any secondary phases. The lattice constants of LLBZT decrease with increasing Ba2+ contents x from 0 to 0.1 while increase with x from 0.1 to 0.3, possibly due to the simultaneous change of Ba2+ and Ta5+substitution levels. Relative densities of LLBZT are in the range between 89% and 93% and not influenced so much by the compositions. From AC impedance spectroscopy measurements, the total (bulk + grain) conductivity at 27ºC of LLBZT has its maximum value of 0.83 mS/cm at x = 0.10, which is slightly higher than the conductivity (= 0.80 mS/cm) of the sample without substituting Ba (x = 0). Activation energy for the conductivity is lowered with increasing Ba substitution levels but excess Ba substitution degrades the conductivity in LLBZT. LLBZT is electrochemically stable at the potential range from 0 to 6.0 V vs. Li+/Li. Moreover, Li+ insertion and extraction reactions of LiMn2O4 (LMO) or TiNb2O7(TNO) film electrode formed on LLBZT by aerosol deposition were confirmed successfully. Particularly, TNO film electrode in all solid state cell with LLBZT showed initial capacities of 220 mAh/g for Li+ insertion and 170 mAh/g for Li+ extraction at 60ºC and 5 mA/g-TNO. These results indicate that cubic garnet-type LLBZT can potentially be used as a solid electrolyte in all-solid-state batteries. Figure 1

Dielectric and piezoelectric properties of (1-x)(K0.474Na0.474Li0.052)(Nb0.948Sb0.052)O3-xBaMO3 (M = Ti or Zr) ceramics

ABSTRACTThe effects of Ba and M (M = Ti or Zr) substitutions for K, Na, Li, Nb and Sb on the ferroelectric and piezoelectric properties of (1-x)(K0.474Na0.474Li0.052)(Nb0.948Sb0.052)O3 (KNLNS)-xBaMO3 ceramics were investigated. X-ray powder diffraction profiles showed the coexistence of rhombohedral-orthorhombic-tetragonal phases, representing a morphotropic phase boundary (MPB), in both (1-x)KNLNS-xBaTiO3 (BT) and (1-x)KNLNS-xBaZrO3 (BZ) ceramics. DSC measurement of (1-x)KNLNS-xBZ ceramics indicated that the Ba and Zr substitutions for A- and B-sites in KNLNS led to the further increase in the dielectric constant in comparison with that of (1-x)KNLNS-xBT ceramics. Moreover, the rhombohedral-orthorhombic phase transition temperature was decreased to room temperature by Ba and Zr substitutions; as a result, a d33 value of 337 pC/N was obtained at 0.94KNLNS-0.06BZ (x = 0.06) ceramic.

Effect of Ba Co-Doping on Sr5(PO4)3Cl:Ce3+ Blue Emitting Phosphor Application for White Light Emitting Diodes

Ce3+-activated Sr5-2x-yBay(PO4)3Cl:xCe3+,xNa+ phosphors were synthesized via the solid statereaction methods. The substitution of Ba2+ for Sr2+ ions was confirmed by Raman spectra. The broadest Raman width in Sr2.45Ba2.45(PO4)3Cl:Ce3+ phosphor supported its highest disorder of the host lattice, leading to the emission spectral broadening with a half width of 95.5 nm due to the larger variation in crystal filed strength. The thermal stability of the luminescence was evaluated by the temperature-dependent luminescence intensity. The simulating a spectra of blue-emitting Sr2.45Ba2.45(PO4)3Cl:0.05Ce3+,0.05Na+ and orange emitting Sr3SiO5:Eu2+ phosphors as light converters, an intense white GaN-based near-UV-LED (400 nm) was exhibit good color-rendering index Ra of 90.8 at a correlated color temperature of 6473 K and CIE coordinates of (0.3165, 0.3051). These characteristics makes Sr2.45Ba2.45(PO4)3Cl: 0.05Ce3+,0.05Na+ should be a promising blue-emitting phosphors for the production of white light in phosphor conversion white-LEDs.

Effect of Ba Co-Doping on Sr5(PO4)3Cl:Ce3+ Blue Emitting Phosphor Application for White Light Emitting Diodes

Spectral broadening of blue apatite phosphors (Sr, Ba)5(PO4)3Cl:Ce3+ was achieved by changing Sr-Ba cation combinations. Their blue emission colors come from the 5d1-4f1 transition of Ce3+ ions, and their excitation bands are ranged from 250 nm to 400 nm. The substitution of Ba2+ for Sr2+ ions was confirmed by Raman spectra. The broadest Raman width in Sr2.45Ba2.45(PO4)3Cl:Ce3+ phosphor supported its highest disorder of the host lattice, leading to the emission spectral broadening with a half width of 95.5 nm due to the larger variation in crystal filed strength. The thermal quenching behavior showed the blue emission maintenance of 80 % around 100°C. Finally, the 400 nm-pumped white-LED was optically simulated so as to achieve an excellent color-rendering index (Ra) of 90 at white color point.