NaSiCon and Related Phases in the Na-Zr-Si-P-O System

Nasicon related phases were reevaluated based on the new experimental information.

1. MALT Literature
   162. Warhus, U., Maier, J., Rabenau, A., J. Solid State Chem. 72, 113-125 1988.
   270.
   
   (a) Pet'kov, VI., Asabina,EA., Markin, AV., Kir'yanov, KV., Thermochmica Acta, 403, 185-196, 2003.
   (b) Pet'kov, VI., Kir'yanov, KV., Orlova, AI., Kitaev, DB., Inorganic Materials 36(4) 387-391 2000.
   (c) Milne, SJ., West, AR., J. Solid State Chem. 57, 166-177 1985.
   (d) Tiets, F., AIMS Materials Science 4(6), 1305-1318 2017.
   (e) Pet'kov, VI., Asabina, EA., Markin, AV., Smirnova, NN., J. Chem. Eng. Data 55, 856-863 2010.
   (f) Yokokawa, H. Estimation from phase relations
   
2. Evaluation
   Based on the phase relations given in 270(d), the thermodynamic data are evaluated to reproduce those relations.
   1. Na-Si-P-O system
      Since the essential feature of the chemical potential diagram for the Na-Si-P-O system constructed using the old MALT data is the same with those phase relations given in 270(d). Three thernary compounds, Na10P2Si4O18, Na18P4Si6O31 and Na15P5Si3O26, are reported in 270(d), but those compounds are not included here.
      
      Fig. 1 CHD Diagram for the Na-Si-P-O system at 1000 K and pO2=1 atm
      
      
      
      
   2. Na-Zr-Si-O system.
      Since some enthalpy changes for formation are given in the NBS table(ref.1), other data are estimated. Heat capacities are assumed to be sum of the contributions from respective constituent oxides.
      • Since for Na2ZrSiO5, HGS are fully available in the table, other data are estimated to reproduce the phase relations in the Na2ZrO3-SiO2.
      • In this evaluation, it comes to realize that the old data of Na2ZrO3 could not give good agreement with the phase relations so that these values are replaced to give more reasonable phase relations.
      • Na6Zr2Si4O15, Na14Zr2Si10O31 are determined so as to appear as stable compounds at lower temperatures.
   3. Na-Zr-P-O system.
      Some enthalpies of formation for Na-Zr-P-O systems are available.
      1. Zr-P-O system:
         
         The thermodynamic properties are evaluated to reproduce the phase relations. Enthalpy change and entropies are estimated from behaviors of other metal phosphates (ref 181).
      2. Na-Zr-P-O System:
         • The series Na1+4xZr2-xP3O12 are isostructure-type and called the NASICON type.
           
         • Based on the enthalpy changes for formation given in 270(a) and 270(b), the thermodynamic properties of NaZr2(PO4)3 and Na5Zr(PO4)3 are determined. Na3Zr1.5(PO4)3 (Na2ZrP2O8) was determined so as to fit to the phase relation given in 270(c). Those compounds correspond to (123, 513, 212) in the abbreviation of Nasicon.
         • The CHD diagram for the Na-Zr-P-O system at 1000 K and pO2=1 atm is given below. The essential parts are in good agreement with phase relations in 270(d).
         • Only one difference can be seen in the tie lie between Na2ZrO3 and (513); in CHD diagram, Na2ZrO3 is not in equilibrim with (513).
         
         
         Fig. 2 CHD Diagram for the Na-Zr-P-O system at 1000 K and pO2=1 atm
         
         
   4. Na-Zr-Si-O system
      The thermodynamic properties of the Na-Zr-Si-O system were examined and modified slightly to reproduce the phase relations given in Fig. 4 of ref. 270(d). Here, data for Na2ZrSi4O12 is lack in the MALT database and there Fig. 3 below does not include this phase.
      
      Fig. 3 CHD Diagram for the Na-Zr-Si-O system at 1273 K and pO2=1 atm
      
      
   5. NaSiCon
      Na1.5Zr2Si0.5P2.5O12, Na3Zr2Si2PO12, Na3.5Zr2Si2.5P.5O12 are estimated so as to apear as stable compounds at 1273 K against the decompsition into Na5Zr(PO4)3 + ZrSiO4. Information given in ref. 162 is neglected.
      
      
      Fig. 4 CHD Diagram for the Na-Zr-Si-P-O system at 1273 K and pO2=1 atm.
      ZrO2(No.54), Na2O2(No.66), Na2ZrO3(No.76) are made transparent. The stability polygons for thpse compounds of Na1.5Zr2Si0.5P2.5O12(No.85), Na3Zr2Si2PO12(No.86), Na3.5Zr2Si2.5P.5O12(No.87) appear between Na5Zr(PO4)3(No.79) and ZrSiO4(No.62)
      

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