This article reports single‐step molten salt synthesis to prepare single‐crystal, platelike NaNbO3 particles without the Bi2O3 byproduct. In the previous method of two‐step molten salt synthesis, platelike Bi2.5Na3.5Nb5O18 particles have been prepared by heating a mixture of Bi2O3,Na2CO3, and Nb2O5 in molten NaCl; the particles are then converted to platelike NaNbO3 particles by reaction with Na2CO3 in molten NaCl. The obtained NaNbO3 particles are polycrystalline, and Bi2O3 particles form as a byproduct. In the present method, single‐crystal, platelike NaNbO3 particles without the Bi2O3 byproduct are obtained by heating mixtures of Bi2O3, Na2CO3, and Nb2O5 with molar ratios of 5:7:10 (the composition of Bi2.5Na3.5Nb5O18) and 5:5:8 (the composition of Bi2.5Na2.5Nb4O15) in molten NaCl at 1225°C for 12 h. During heating, platelike Aurivillius (Bi2.5Na3.5Nb5O18 and Bi2.5Na2.5Nb4O15) particles are formed first and these then react with NaCl to form platelike NaNbO3 particles, BiCl3, and Na2O. BiCl3 evaporates from the system and Na2O is washed out after heating. Thus, single‐phase NaNbO3 is obtained. Sluggish conversion from the Aurivillius phases to NaNbO3 is responsible for the formation of single‐crystal particles.

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The preparation of platelike NaNbO 3 grains via single-step molten salt synthesis using Bi 2 O 3 , Na 2 CO 3 , Nb 2 O 5 , and NaCl as reactants was examined. When a new alumina crucible was used, platelike NaNbO 3 grains were obtained, but a repeatedly used alumina crucible resulted in irregularly shaped NaNbO 3 grains. When a platinum crucible was used, even NaNbO 3 could not be obtained. Addition of alumina substrates and alumina granules to the reaction mixture in the platinum crucible resulted in the formation of platelike NaNbO 3 grains and second-phase grains. The second-phase grains, which were composed of Al 2 O 3 , Bi 2 O 3 , Na 2 O, and Nb 2 O 5 and had a pyrochlore structure, could be removed by sieving. The second phase acted as a scavenger for Bi 2 O 3 and hence, the possibility of using another scavenger was attempted. The new scavenger was a mixture of Na 2 CO 3 and Nb 2 O 5 , and using them, platelike NaNbO 3 grains were successfully obtained with NaNb 5 Bi 2 O 16 as a byproduct, which could then be removed by sieving.

The development of grain orientation was examined for (K,Na)NbO 3 -based ceramics using two kinds of platelike NaNbO 3 template powders made by single-and two-step molten salt synthesis (MSS) and four kinds of matrix powders to examine the factors controlling the degree of orientation. The template grains made by single-step MSS were dissolved in the matrix of a mixture of NaNbO 3 and KNbO 3 powders, leaving large voids. The template grains made by two-step MSS were not dissolved and gave high reproducibility in the degree of orientation. The effect of matrix species on the grain orientation was examined using the template powder made by two-step MSS and the matrixes of KNbO 3 , NaNbO 3 , and (K 0.5 Na 0.5 )NbO 3 powders and a mixture of KNbO 3 and NaNbO 3 powders. The extensive grain orientation developed only in (K 0.5 Na 0.5 )NbO 3 and a mixture of KNbO 3 and NaNbO 3 powders. The origin of the difference in the grain orientation behavior was examined by microstructure observation.