High temperature protonic conduction in LaPO4 doped with alkaline earth metals

Amezawa, Koji; Tomii, Yoichi; Yamamoto, Naoichi

doi:10.1016/j.ssi.2004.07.003

Cited by 54 publications

(87 citation statements)

References 13 publications

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“…Figure 5 shows the electrical conductivity of La 1-x Sr x P 5 O 14-δ as a function of oxygen partial pressure at 573, 623 and 673 K. It was found that the electrical conductivity was independent of oxygen partial pressure in the oxygen partial pressure and temperature ranges investigated. This tendency is similar to the other phosphate based protonic conductors such as La 0.99 Sr 0.01 PO 4-δ [17] and La 0.97 Sr 0.03 P 3 O 9-δ [19]. Figure 6 compares the electrical conductivities of La 1-x Sr x P 5 O 14-δ in 1.0×10 −2 atm hydrogen-1.2×10 −2 atm water vapor, unhumidified 1.0×10 −2 atm oxygen and unhumidified 1.0×10 −2 atm hydrogen as a function of inverse temperature.…”

Section: Specimenssupporting

confidence: 83%

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Electrical conductivities of strontium-doped rare earth ultraphosphates and oxyphosphates

2012

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Electrical conductivity of lanthanum ultraphosphate and neodymium oxyphosphate both doped with strontium, La 1-x Sr x P 5 O 14-δ (x00, 0.01, 0.03 and 0.05 in nominal formulae) and (Nd 1-x Sr x ) 3 PO 7-δ (x00 and 0.03), respectively, was investigated with a two-probe ac technique. The electrical conductivity was measured as functions of oxygen partial pressure and water vapor pressure in the temperature range of 523 to 673 K for the former and 973 to 1273 K for the latter. La 1-x Sr x P 5 O 14-δ have considerable protonic conductivity, which was evidenced by isotope effect of hydrogen and deuteron on the electrical conductivity, over the wide range of oxygen partial pressure such as oxygen and hydrogen containing atmospheres. La 1-x Sr x P 5 O 14-δ exhibit protonic conductivities of 4.7×10 −5 −2.2×10 −3 S cm −1 in the temperature range of 523-673 K, which is comparable to the other phosphate based protonic conductors. Although protonic defects are considered to be induced and a major positive defect in (Nd 0.97 Sr 0.03 ) 3 PO 7-δ , attributed to small protonic mobility, (Nd 0.97 Sr 0.03 ) 3 PO 7-δ is a mixed oxide ion and electron hole conductor at 1173-1273 K, then, it turns to be electron hole conductor below temperatures of 1073 K. (Nd 0.97 Sr 0.03 ) 3 PO 7-δ in 1.0×10 −2 atm oxygen-1.9× 10 −2 atm water vapor had smaller conductivity than that in unhumidified 1.0×10 −2 atm oxygen. The conductivities were 9.7×10 −3 −3.1×10 −1 S cm −1 and 2.8×10 −3 −2.5×10 −1 S cm −1 in the above gases, respectively, in the temperature range of 973-1273 K. (Nd 0.97 Sr 0.03 ) 3 PO 7-δ had larger activation energy such as 165 kJ mol −1 than proton conducting La 1-x Sr x P 5 O 14-δ (76 kJ mol −1 ) including other proton conducting phosphates (68-86 kJ mol −1 ).

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Section: Specimenssupporting

confidence: 83%

“…Some acceptor-doped ceramics such as perovskite-type oxides [1][2][3][4][5][6][7][8][9][10], phosphates [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], borates [27], niobates and tantalates [28] etc. are known to significantly conduct protons at high temperatures.…”

Section: Introductionmentioning

confidence: 99%

Electrical conductivities of strontium-doped rare earth ultraphosphates and oxyphosphates

2012

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“…Y doped Ce(PO 3 ) 4 had higher conductivity than other materials. In previous works [1][2][3], the dopant, which has a little larger ionic radius than original material, much improved the conductivity of phosphate. The ionic radius is Ce>Gd>Y>Yb, on the other hand, the results of electrical conductivity in this work was Y-doped>undoped>Yb nearly equal Gd doped material.…”

Section: Synthesis Of Cerium Polyphosphate Bulksmentioning

confidence: 98%

“…Solid oxide fuel cell (SOFC) and polymer electrolyte fuel cell (PEFC) are well known and investigated to work at high and low temperature, respectively. At the middle temperature, phosphate material works as a solid state electrolyte [1][2][3].…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Electrical Conductivity of Tetra-Valent Cerium Polyphosphate Bulks

Onoda

Inagaki

Kuwabara

et al. 2009

Phosphorus Research Bulletin

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Tetra-valent cerium phosphate was synthesized from cerium oxide and phosphoric acid by heating. The sintering processes, pressure-less sintering (PLS), spark plasma sintering (SPS), and hydrothermal hot pressing (HHP), were tried to obtain polyphosphate bulks. Furthermore, the electrical conductivity of cerium polyphosphate bulks was investigated. Tetra-valent cerium phosphate was synthesized by heating at 700ºC for 20 hours. The hydrothermal hot pressing process was the suitable method to synthesize the tetra-valent cerium phosphate bulk. Y doped Ce(PO 3 ) 4 had higher conductivity than other rare earth phosphates. A part of tetra-valent cerium cation was considered to reduce tri-valent cerium cation and then to work as a dopant.

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“…1. Single-phase LaP 3 O 9 precipitated from every solution in the case of C init = 10, while the secondary phases of NaLa(PO 3 ) 4 or MgP 2 O 6 precipitated with LaP 3 O 9 from Na or Mg-containing solutions, in the case of C init . = 20.…”

Section: Resultsmentioning

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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High temperature protonic conduction in LaPO4 doped with alkaline earth metals

Cited by 54 publications

References 13 publications

Electrical conductivities of strontium-doped rare earth ultraphosphates and oxyphosphates

Electrical conductivities of strontium-doped rare earth ultraphosphates and oxyphosphates

Synthesis and Electrical Conductivity of Tetra-Valent Cerium Polyphosphate Bulks

Exploration of Dopant Species for Lanthanum Polyphosphate

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