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Bromide (Br−) ion conductivity in the LaOBr-type solid was successfully improved by partial replacement of the La3+ ion sites in LaOBr with lower valent Zn2+ and Sr2+ ion. Here, Zn2+ ion having high electronegativity was introduced together with Sr2+ ion to form large number of Br− ion vacancies for Br− ion migration, since higher electronegativity of cation is effective for building a strong bond with the surrounding anions inside the LaOBr lattice. As a result, a high concentration of Br− vacancies was successfully introduced with prohibiting the lattice collapse, and the extraordinary high Br− ion conductivity was obtained for the La0.80Sr0.15Zn0.05OBr0.80 solid. [ABSTRACT FROM AUTHOR]

Divalent ion-conducting solid electrolytes with NASICON-type three-dimensional network structures (MxHf1−x)4/(4−2x)Nb(PO4)3 (M = Ni, Mg, Ca, Sr) were successfully developed by introducing M2+ cations into HfNb(PO4)3 solids. The presence of high-valence cations such as Hf4+, Nb5+, and P5+ in the structures effectively reduced the electrostatic interaction between the conducting M2+ cations and the surrounding oxide anions, enabling the M2+ cations to migrate smoothly in the rigid crystal lattice. The relationship between the cation conductivity in NASICON-type solids and the ionic radius of the migrating divalent cation species was also clarified by taking into account the relative sizes of the conduction pathways in the structures. [ABSTRACT FROM AUTHOR]

A new nitrogen monoxide (NO) gas sensor was fabricated from a combination of trivalent aluminum cation- and divalent oxide anion-conducting solid electrolytes, with potassium nitrite-doped gadolinium oxide solid solution serving as the NO sensing auxiliary electrode. The sensor exhibits rapid response, and provides a continuous and reproducible output. The sensor output shows close agreement with the Nernst equation, thereby demonstrating quantitative NO detection. [Copyright &y& Elsevier]

A chlorine gas sensor was fabricated from monovalent Cl− anion- and trivalent Sc3+ cation-conducting solid electrolytes. The sensor exhibited reproducible response, and time to reach 90% response was less than 3 min. Good linearity was observed between the sensor EMF output and the logarithm of the chlorine gas concentration, and the results obey ideal Nernst equation. [Copyright &y& Elsevier]

A cerium ion conducting solid electrolyte, (CexZr1−x)4/4−xNb(PO4)3, was successfully realized with the NASICON-type structure which possesses a three-dimensional network, especially suitable for bulky ion migration. The cerium ion conductivity exceeds approximately one order of magnitude in comparison to that of the rare-earth ion conducting R2(WO4)3 and R1/3Zr2(PO4)3 (R=Sc, Y, Eu–Lu) series and the value is in the range between typical oxide anion conductors of yttria stabilized zirconia (YSZ) and calcia stabilized zirconia (CSZ). Since cerium ion has been demonstrated to be another migrating ion species in solid electrolyte field, a promising application for various functional materials is greatly expected. [Copyright &y& Elsevier]

Abstract: A solid electrolyte type SO2 gas sensor based on tetravalent Zr4+ ion conducting Zr39/40TaP2.9W0.1O12 and O2− ion conducting (ZrO2)0.92(Y2O3)0.08 solid electrolytes with 0.7La2O2SO4–0.3(0.8Li2SO4 +0.2K2SO4) as an auxiliary sensing electrode was developed. The present sensor exhibited a continuous, reproducible, and quantitative response for SO2 gas, and the relationship between the sensor EMF output and the logarithm of the SO2 gas concentration obeyed the Nernst equation at temperatures as low as 480°C over 80 days. Thus, it is expected to be a good candidate as a practical SO2 gas sensor for on site measurements. [Copyright &y& Elsevier]

Abstract: Ammonia gas sensors were fabricated by using trivalent aluminum ion conducting (Al0.2Zr0.8)20/19Nb(PO4)3 solid electrolyte with aluminum metal film as a reference electrode. As the auxiliary sensing electrode material, praseodymium ammonium double sulfate Pr2(SO4)3·(NH4)2SO4 or (NH4)2HPO4 doped La2O2SO4 solid solution, 0.7La2O2SO4–0.3(NH4)2HPO4, was applied from the view points of thermal stability or water durability. The former sensor with Pr2(SO4)3·(NH4)2SO4 showed a rapid response and the latter one with 0.7La2O2SO4–0.3(NH4)2HPO4 exhibited a theoretical response even in a humid atmosphere. Since the present sensors applying Al3+ ion conductor showed such a high sensing performance of rapid response or high durability for water, it is greatly expected to be practical NH3 gas sensors. [Copyright &y& Elsevier]

Abstract: A solid electrolyte type nitrogen oxides (NO x ) gas sensor was fabricated by applying an Al3+ cation conducting solid electrolyte with the KNO3-doped (Gd0.4Nd0.6)2O3 solid solution and Al metal as the auxiliary sensing electrode and the reference electrode, respectively. A rapid, reproducible and continuous sensor response was obtained with obeying the theoretical Nernst relationship for NO and NO2 gases at the temperature as low as 250°C, one of typical temperature of emitted gases. [Copyright &y& Elsevier]

Abstract: A new type of lithium ion conducting solid electrolyte based on a cubic rare earth oxide was developed by co-doping LiNO3 and KNO3 into a (Gd1−x Nd x )2O3 solid, which possesses large interstitial open spaces within the structure. Among the samples prepared, 0.6(Gd0.4Nd0.6)2O3–0.16LiNO3–0.24KNO3 exhibits the highest lithium ion conductivity of 8.05×10−2 and 1.35×10−3 Scm−1 at 400 and 100°C, respectively, which is comparable to that of the LISICON materials. Pure Li+ ion conduction was successfully demonstrated by the dc electrolysis method. [Copyright &y& Elsevier]

Abstract: A new type of potassium ion conducting polycrystalline solid electrolyte, (1− x)La2O2SO4 − x(0.8K2SO4 −0.2CaSO4), with the high ion conductivity at the elevated temperature region was developed by doping potassium and calcium sulfates into the thermally stable lanthanum oxysulfate. Among the samples of the single phase La2O2SO4, the 0.8La2O2SO4 −0.2(0.8K2SO4 −0.2CaSO4) (x =0.2) shows the highest ion conductivity reaching values potentially suitable for applications, i.e. σ is greater than 10−2 Scm−1 above 800°C. [Copyright &y& Elsevier]

Abstract: Two types of polycrystalline solids, KNO2 mixed Gd2O3 and KNO2 mixed Nb2O5, were prepared. In the case for KNO2 mixed Gd2O3, a remarkable enhancement in K+ ion conductivity was successfully realized by interstitially dissolved KNO3 formed during the preparation process in the C-type cubic Gd2O3 crystal lattice. In contrast, the conductivity of KNO2 mixed Nb2O5 was more than three orders of magnitude below that of the Gd2O3–KNO3 solid solution due to the KNO3 decomposition during the preparation procedure. The K+ ion conductivity of the polycrystalline Gd2O3–KNO3 solid solution is more than three orders of magnitude higher than that of the K+ ion conducting K2SO4 polycrystal and the value exceeds that of K+-β′′-alumina single crystal in ab plane, realizing the highest ion conductivity among the K+ ion conducting solid electrolyte series. The superior ion conducting properties are realized by forming the interstitially KNO3 dissolved Gd2O3 solid solution, without decomposing the mixed salt with K+. [Copyright &y& Elsevier]

Abstract: High halide ion conduction in a solid was realized for the La1−x M x O(Cl1−y Br y )1−x solid solution (M: alkaline earth metal). The ion conductivity in LaOCl1−y Br y increased by partially replacing the La3+ site with Sr2+ and the highest halide ion conductivity of 1.2×10−2 Scm−1 at 600°C was obtained for La0.85Sr0.15O(Cl0.8Br0.2)0.85, which was 2.2 and 6.2 times higher than those for La0.8Ca0.2OCl0.8 and La0.9Sr0.1OBr0.9, respectively. The conducting ion species in the La0.85Sr0.15O(Cl0.8Br0.2)0.85 solid solution were directly identified to be Cl− and Br− ions by the dc electrolysis method. [Copyright &y& Elsevier]

Scandium oxide single crystals were successfully grown electrochemically by applying the Sc3+ ion-conducting Sc2(MoO4)3 solid electrolyte at 1223 K. The single crystal growth can be regulated by the electrolysis condition, and the crystal size can be intentionally controlled by adjusting the electrolysis period. Although the single crystal growth of such refractory oxides as Sc2O3 is considerably difficult by the conventional thermal heating-cooling crystal growth procedure because of the high melting point of Sc2O3 (ca. 2823 K), the electrochemical single crystal growth presented in this study can be simply applicable at moderate temperatures around 1273 K for the single crystal growth. This method is also available to the other rare earth oxides by applying a series of Ln2(MoO4)3 solid electrolytes in which the target rare earth ion conducts. [Copyright &y& Elsevier]

A new type of potassium ion conducting polycrystalline solid electrolyte was prepared by forming the Gd2O3–KNO2 solid solution. Since KNO2 is dissolved in the Gd2O3 crystal lattice scale, a considerable enhancement in K+ ion conductivity was successfully realized. The K+ ion conductivity is more than three orders of magnitude higher than that of the well-known K+ ion conducting K2SO4 polycrystal solid and the value also exceeds that of K+–β″-alumina single crystal, demonstrating the highest ion conductivity among the K+ ion conducting solid series. [Copyright &y& Elsevier]

Abstract: A new solid electrolyte type sulfur dioxide gas sensor was fabricated by the combination of the trivalent aluminum cation conducting (Al0.2Zr0.8)20/19Nb(PO4)3 solid and the divalent oxide anion conducting yttria stabilized zirconia (YSZ) with the NaAl(SO4)2 solid as a detecting auxiliary electrode. Since the present sensor showed such a superior sensing performance of theoretical response, which obeys the Nernst relationship between the sensor EMF output and the logarithm of the SO2 gas concentration, along with the stable, continuous, and reproducible response, it is greatly expected to be applied to a practical SO2 gas sensing device. [Copyright &y& Elsevier]

Highlights • (Ni x Hf 1− x) 4/(4−2 x) Nb(PO 4) 3 solid was synthesized by conventional co-precipitation method. • The synthesized (Ni x Hf 1− x) 4/(4−2 x) Nb(PO 4) 3 solid has three dimensional NASICON-type structure. • High Ni2+ ion conductivity and low activation energy were realized. Abstract Divalent Ni2+ cation-conducting solid electrolytes, (Ni x Hf 1− x) 4/(4−2 x) Nb(PO 4) 3 , were successfully developed by introducing Ni2+ cations into a HfNb(PO 4) 3 solid exhibiting a three-dimensional NASICON-type structure. Although the HfNb(PO 4) 3 solid has been reported to be purely a Hf4+ ion conductor, the conducting species was changed to the divalent Ni2+ cation upon Ni2+ doping, due to the facile migration of lower-valence ions in the rigid crystal lattice. In addition, by selecting the well-ordered NASICON-type structure as the mother crystal, the (Ni x Hf 1− x) 4/(4−2 x) Nb(PO 4) 3 solid electrolytes exhibited lower activation energies and higher Ni2+ cation conductivities than a previously reported NiZr 4 (PO 4) 6 solid with the β-Fe 2 (SO 4) 3 -type structure. Among the (Ni x Hf 1− x) 4/(4−2 x) Nb(PO 4) 3 solids, (Ni 0.06 Hf 0.94) 4/3.88 Nb(PO 4) 3 (x = 0.06) showed the highest Ni2+ ion conductivity, of 2.27 × 10−4 S·cm−1 at 600 °C, which is ca. 23 times higher than that of the NiZr 4 (PO 4) 6 solid. [ABSTRACT FROM AUTHOR]

A three-dimensionally well-ordered NASICON-type Mg 2+ cation conductor, (Mg x Hf 1− x ) 4/(4−2 x ) Nb(PO 4 ) 3 , was firstly developed by partial substitution of lower valent Mg 2+ cation onto the Hf 4+ sites in a HfNb(PO 4 ) 3 solid to realize high Mg 2+ cation conductivity even at moderate temperatures. Due to the formation of well-ordered NASICON-type structure, both the high Mg 2+ cation conductivity below 450 °C and the low activation energy for Mg 2+ cation migration was successfully realized for the (Mg 0.1 Hf 0.9 ) 4/3.8 Nb(PO 4 ) 3 solid. Pure Mg 2+ cation conduction in the NASICON-type (Mg 0.1 Hf 0.9 ) 4/3.8 Nb(PO 4 ) 3 solid was directly and quantitatively demonstrated by means of two kinds of dc electrolysis. [ABSTRACT FROM AUTHOR]

Abstract: Single crystals of non-stoichiometric terbium oxide δ-Tb11O20 (TbO1.818) were successfully grown by direct current (dc) electrolysis of a Tb3+ ion conducting Tb2(MoO4)3 solid electrolyte at 3V and 900°C under a low oxygen partial pressure, =1×10−5 MPa. Selected-area electron diffraction patterns for the particles prepared by the electrolysis corresponded to that of δ-Tb11O20 (TbO1.818). Tb11O20 forms triclinic crystals in the space group with a =6.51Å, b =9.83Å, c =6.49Å, α =90.02°, β =99.97°, and γ =95.88°. The crystal size can be intentionally controlled by adjusting the electrolysis period. The average particle sizes were 0.69 and 1.70μm for a week and 3 weeks electrolysis, respectively. [Copyright &y& Elsevier]

Abstract: Single crystals of non-stoichiometric terbium oxide Tb24O44 (≡TbO1.833) were successfully grown by the dc electrolysis of the Tb3+ ion conducting Tb2(MoO4)3 solid electrolyte at the moderate conditions of 3V at 900°C. Electron diffraction patterns for each particle grown clearly indicate that the particles were single crystals of the β2-phase of high quality Tb24O44 (≡TbO1.833). Tb24O44 is triclinic of space group with a =6.49Å, b =12.27Å, c =12.43Å, α =78.51°, β =99.82° and γ =71.12°. The crystal size can be intentionally controlled by adjusting the electrolysis period: the average particle sizes were 0.40, 0.65 and 1.52μm for 1, 2 and 4 weeks electrolysis, respectively. [Copyright &y& Elsevier]

• Mg2+ and Sr2+ were introduced into LaOBr to control Br− vacancy and bond strength. • Mg2+ with low electronegativity weakened the bond strength between Br and La. • The adjustment of the electronegativity of cation dopant improved Br− conductivity. In this study, the bromide ion conduction in the LaOBr based solids was successfully improved by introducing Mg2+ with a smaller ionic size and lower electronegativity into the La3+ site of LaOBr doped with larger Sr2+ to simultaneously control the amount of Br− vacancies and the bond strength of Br− with surrounding cations. Among the La 1− x − y Sr y Mg x OBr 1− x − y solids prepared, La 0.80 Sr 0.15 Mg 0.05 OBr 0.80 exhibited the highest Br− conductivity of 6.5 × 10−2 S·cm−1 at 800 °C, which is ca. two times higher than that of the La 0.80 Sr 0.15 Zn 0.05 OBr 0.80 with a similar lattice volume and the same amount of Br− vacancies. The improvement in the Br− conductivity is explained from the viewpoint of topical structural strain caused by the doping of Mg2+ with low electronegativity. [ABSTRACT FROM AUTHOR]