Understanding Na Mobility in NASICON Materials: A Rietveld, 23Na and 31P MAS NMR, and Impedance Study
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- 作者：Enrique R. Losilla ; Miguel A. G. Aranda ; Sebastiá ; n Bruque ; Miguel A. Parí ; s ; Jesú ; s Sanz ; and Anthony R. West
- 刊名：Chemistry of Materials
- 出版年：1998
- 出版时间：February 1998
- 年：1998
- 卷：10
- 期：2
- 页码：665 - 673
- 全文大小：138K
- 年卷期：v.10,no.2(February 1998)
- ISSN：1520-5002
文摘
The structures and electrical properties of four NASICONcompositions,Na1.4M1.6In0.4(PO4)3 (M = Ti, Sn, Hf, Zr), have beendetermined and compared. Rietveld refinement ofpowder X-ray diffraction data confirmed the basic rhombohedral NASICONstructure withrandom occupancy of the octahedral In/M sites, full occupancy of theNa(1) sites and partialoccupancy of the Na(2) sites. For three compositions, M =Zr, Sn, and Hf, the 31P MASNMR peak intensities of the four detected signals, attributed to fourdifferent phosphorusenvironments[P(OM)4-n(OIn)n(n = 0-3)], were close to the ratios expected for arandomdistribution of In/M. For M = Ti, some departures fromstatistical occupancy were apparent.23Na MAS NMR data gave evidence for twoNa+ positions at room temperature for M =Ti,Sn, attributable to occupation of Na(1) and Na(2) sites.For M = Hf, Zr, only a single signalcould be resolved at room temperature, which splits into two signals oncooling to - 50 
ntities/deg.gif">C,indicating high Na mobility at room temperature. Impedance dataobtained on pressedsintered pellets over the range 25-300 ntities/deg.gif">C showed that bulk ionicconductivities increasedand activation energies decreased in the sequence Ti, Sn, Hf, Zr.The geometry of the M1M2bottleneck has been determined from structural data, and a directcorrelation found betweenactivation energy for ion conduction and the bottlenecksize.
ntities/deg.gif">C,indicating high Na mobility at room temperature. Impedance dataobtained on pressedsintered pellets over the range 25-300 ntities/deg.gif">C showed that bulk ionicconductivities increasedand activation energies decreased in the sequence Ti, Sn, Hf, Zr.The geometry of the M1M2bottleneck has been determined from structural data, and a directcorrelation found betweenactivation energy for ion conduction and the bottlenecksize.