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T. Okura and K. Yamashita
the abovementioned devices utilize the dc conduction properties of Na + superionic
conductors, another aim was to study the microstructural effects on the conduction
properties of a whole glass-ceramic [24–28]. Special attention was paid to the
analysis of grain boundary properties using the Na 2 O-Y 2 O 3 -P 2 O 5 -SiO 2 system.
For the analysis of grain boundary properties, as discussed below, composition
dependences on the conductivity of sodium silicophosphate glasses containing
Y 2 O 3 were also introduced in the Na 2 O-Y 2 O 3 -P 2 O 5 -SiO 2 system. For convenience,
the present materials are abbreviated as Narpsio, taken from the initials of the Na 2 OR 2 O 3 -P 2 O 5 -SiO 2 system.
10.2 Materials
10.2.1 Glasses and Glass-Ceramics
We successfully produced the Narpsio family by the following methods: (i)
solid-state reactions of powders [10, 22], (ii) sol-gel method [19, 29], and (iii)
crystallization of glasses [30]. In considering practical applications such as Na/S
batteries, the present Narpsio materials may be expected to show advantages over
the aluminas, both in lowering the heat treatment temperatures and in fabricating
various shapes because of the ease of glass-making. The latter point closely depends
on the glass-ceramic processing technology.
Precursor glasses were prepared from reagent-grade oxides of anhydrous
Na 2 CO 3 , R 2 O 3 (R = Y, Sc, In, Er, Gd, Sm, Eu, Nd, La), NH 4 H 2 PO 4 , and SiO 2 ; the
mechanically mixed powders according to formula 2 or appropriate compositions
shown below were melted at 1350 ◦ C for 1 h after calcination at 900 ◦ C for 1 h. The
melts were quickly poured into a graphite cylinder and then annealed at 500 ◦ C for
3 h, giving Narpsio glasses. The composition parameters studied were in the range
of 0.2 < x < 0.6 and 0 < y < 0.5 of formula 2. As shown below, grain boundary
conduction properties are discussed in relation to the properties of glasses. For
the evaluation of the composition dependence of conductivity in Na + conducting
glasses, various sodium-yttrium silicophosphate glass specimens with different
atomic ratios of Na/(P+Si) and Na/Y were also prepared.
Crystallization was carried out according to a previous report [14]; bulk glasses
were heated at a rate of 75 ◦ C/h to a temperature approximately 50 ◦ C above the
glass transition point, which had been determined in advance by differential thermal
analysis (DTA). This pretreatment was performed in order to obtain homogeneous
nucleation [23]. After annealing for 1 h, the specimens were heated at temperatures
of 800–1100 ◦ C, depending on the composition, for 0.5 to 72 h, and thereafter slowly
cooled in a furnace with a decreasing rate of 150 ◦ C/h to room temperature. These
quenched glasses or glass-ceramic specimens were polished with 0.5 μm diamond
paste and thereafter subjected to conductivity measurements.
T. Okura and K. Yamashita
the abovementioned devices utilize the dc conduction properties of Na + superionic
conductors, another aim was to study the microstructural effects on the conduction
properties of a whole glass-ceramic [24–28]. Special attention was paid to the
analysis of grain boundary properties using the Na 2 O-Y 2 O 3 -P 2 O 5 -SiO 2 system.
For the analysis of grain boundary properties, as discussed below, composition
dependences on the conductivity of sodium silicophosphate glasses containing
Y 2 O 3 were also introduced in the Na 2 O-Y 2 O 3 -P 2 O 5 -SiO 2 system. For convenience,
the present materials are abbreviated as Narpsio, taken from the initials of the Na 2 OR 2 O 3 -P 2 O 5 -SiO 2 system.
10.2 Materials
10.2.1 Glasses and Glass-Ceramics
We successfully produced the Narpsio family by the following methods: (i)
solid-state reactions of powders [10, 22], (ii) sol-gel method [19, 29], and (iii)
crystallization of glasses [30]. In considering practical applications such as Na/S
batteries, the present Narpsio materials may be expected to show advantages over
the aluminas, both in lowering the heat treatment temperatures and in fabricating
various shapes because of the ease of glass-making. The latter point closely depends
on the glass-ceramic processing technology.
Precursor glasses were prepared from reagent-grade oxides of anhydrous
Na 2 CO 3 , R 2 O 3 (R = Y, Sc, In, Er, Gd, Sm, Eu, Nd, La), NH 4 H 2 PO 4 , and SiO 2 ; the
mechanically mixed powders according to formula 2 or appropriate compositions
shown below were melted at 1350 ◦ C for 1 h after calcination at 900 ◦ C for 1 h. The
melts were quickly poured into a graphite cylinder and then annealed at 500 ◦ C for
3 h, giving Narpsio glasses. The composition parameters studied were in the range
of 0.2 < x < 0.6 and 0 < y < 0.5 of formula 2. As shown below, grain boundary
conduction properties are discussed in relation to the properties of glasses. For
the evaluation of the composition dependence of conductivity in Na + conducting
glasses, various sodium-yttrium silicophosphate glass specimens with different
atomic ratios of Na/(P+Si) and Na/Y were also prepared.
Crystallization was carried out according to a previous report [14]; bulk glasses
were heated at a rate of 75 ◦ C/h to a temperature approximately 50 ◦ C above the
glass transition point, which had been determined in advance by differential thermal
analysis (DTA). This pretreatment was performed in order to obtain homogeneous
nucleation [23]. After annealing for 1 h, the specimens were heated at temperatures
of 800–1100 ◦ C, depending on the composition, for 0.5 to 72 h, and thereafter slowly
cooled in a furnace with a decreasing rate of 150 ◦ C/h to room temperature. These
quenched glasses or glass-ceramic specimens were polished with 0.5 μm diamond
paste and thereafter subjected to conductivity measurements.