Precipitation behavior of highly Sr-doped LaPO4 in phosphoric acid solutions

Hatada, Naoyuki; Nosé, Yukihiko; Kuramitsu, Akiko; Uda, Tetsuya

doi:10.1039/c0jm03171b

Cited by 13 publications

(19 citation statements)

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“…[12][13][14][15] Unfortunately it is known that the electrical conductivity in a wet condition is lower in the phosphate compared with the barium zirconate, but it is noteworthy that a recent work indicated the increase of the Sr-substitution amount-in other words, proton concentration in the crystal-by applying a liquid phase method for the material preparation. 16 Some researches also have devoted their efforts to LaBaGaO 4 -based protonic conductors with the B-K 2 SO 4 -type structure, and have demonstrated that they exhibit protonic conductivity above 10 ¹4 S·cm ¹1 at 500°C. 17,18 In the case of La 1¹x Ba 1+x GaO 4¹D , a substitution of the lower cation (Ba 2+ ) to the La 3+ site causes the oxygen-vacancy formation, and then the proton defects were produced in the crystal structure by incorporating ambient water vapor into the oxygen vacancy, according to the following defect equation and equilibrium: In this study, we aim to increase the protonic conductivities of La 1¹x Ba 1+x GaO 4¹D by preparation with a liquid-phase method.…”

Section: Introductionmentioning

confidence: 99%

Study of Crystal Structure and Protonic Conduction Properties of La0.9Ba1.1GaO4^|^minus;^|^delta; Prepared by Liquid Synthesis Method

et al. 2014

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In order to investigate an effect of the preparation process on protonic conductivity of La 1−x Ba 1+x GaO 4−δ , we attempt to prepare the samples with x = 0.1, La 0.9 Ba 1.1 GaO 4−δ , by a liquid synthesis method as well as a conventional solid-phase method. Their electrical conductivities are measured from 300 to 900°C in various water vapor partial pressures, P H 2 O . From the result, it is found that the protonic conductivity is higher in the sample synthesized by the liquid synthesis method compared with that by the solid-phase method. In addition, it is also indicated that the P H 2 O -dependence of the electrical conductivity around 600°C is more significant in the sample prepared by the liquid synthesis method. This result implies that this method enhances proton dissolution in La 0.9 Ba 1.1 GaO 4−δ at least around the temperature range. To investigate a crystal structure change by the synthesis method, we perform powder neutron diffraction measurements. The Rietveld and maximum entropy method (MEM) analyses demonstrate that nuclear density of the proton is clearly observed between neighboring O3 sites, and suggest that the liquid synthesis method makes a site occupancy of proton higher.

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Section: Introductionmentioning

confidence: 99%

Study of Crystal Structure and Protonic Conduction Properties of La0.9Ba1.1GaO4^|^minus;^|^delta; Prepared by Liquid Synthesis Method

et al. 2014

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“…It has been reported that the doping level of Sr-doped LaPO 4 synthesized by precipitation method depends on precipitation period. 18 Thus, doping levels in LaP 3 O 9 were derived from the average compositions of whole precipitates analyzed by ICP-AES.…”

Section: Methodsmentioning

confidence: 99%

“…For example, higher doping levels can be achieved. 10,18 Additionally, larger and c-axisoriented grains can be obtained, 19 while grains are randomly oriented in the case of SSR. Larger grains reduce the density of grain boundary, which generally has an unignorable resistance against proton conducz E-mail: adachi.yoshinobu.36z@st.kyoto-u.ac.jp tion, and c-axis orientation enhances the bulk conductivity, because c-axis has one of the highest conductivities in LaP 3 O 9 crystal.…”

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confidence: 99%

Exploration of Dopant Species for Lanthanum Polyphosphate

Adachi

Hatada

Kuramitsu

et al. 2015

J. Electrochem. Soc.

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Doped lanthanum polyphosphate (LaP 3 O 9 ) exhibits relatively high proton conductivity. For the practical applications such as the electrolyte of fuel cells, however, its conductivity must be improved by 2 orders of magnitude. Protons are introduced into matrix by lower-valent cation doping, and proton conductivity depends on dopant species. To date, LaP 3 O 9 has been doped with only Ca, Sr and Ba. In this work, we tried to dope LaP 3 O 9 with Na + , K + , Mg 2+ and Pb 2+ , as the new dopant species, due to their close ionic radii to La 3+ . Among them, only Pb could substitute for La at a comparable concentration to those of alkaline earth metals and its highest doping level was 6.4 mol% (Doping level is defined as the concentration ratio of dopant (M) to host cation (La) site in matrix (≡M/(La + M) × 100 (mol%))). Though Pb can exist as either divalent or tetravalent state, Pb in LaP 3 O 9 was identified to be divalent state by XPS analysis. Proton conduction was demonstrated by H/D isotope effect. The electrical conductivity of Pb-doped LaP 3 O 9 increased with Pb-doping level, owing to the increase in proton concentration. The conductivity of 4.5 mol% Pb-doped LaP 3 O 9 was about one order of magnitude lower than that of 7.9 mol% Sr-doped LaP 3 O 9 .

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“…[10] Therefore, divalent (Ca 2+ , Sr 2+ )-doped LaPO4 has been investigated as a prospective protonic conductive material. [11][12][13] Interestingly, the published research reports widely varying Sr substitutional concentrations [11,[14][15][16][17] which may be due to different (OH) -content.…”

Section: +mentioning

confidence: 99%

“…Sr-doped LaPO4 has been synthesized via several methods with widely varying maximum Sr concentrations: Microwave assisted hydrothermal processes (SrLa ~2%) [ 19 ] , homogeneous precipitation in a controlled atmosphere (SrLa ~20%) [ 15 ] , co-precipitation of La and Sr phosphates using (NH4)2HPO4, La(NO3)3 and Sr(NO3)2 aqueous solutions (SrLa ~7%) [ 11 ] , calcination where SrHPO4 and LaPO4 are mixed and calcined at 1000ºC (SrLa ~1%).…”

Section: If (Oh)mentioning

confidence: 99%