Consolidation, Microstructure and Crystallography of Dense NaNbO₃ Ceramics with Ultra-Fine Grain Size

Abstract

Paper péÉÅá~ä fëëìÉ Äó dìÉëí bÇáíçêë aÉÇáÅ~íÉÇ íç mêçÑK d äìåíÉê mÉíòçïW jçÇÉêå qêÉåÇë áå^Çî~åÅÉÇ`Éê~ãáÅë çåëçäáÇ~íáçå, jáÅêçëíêìÅíìêÉ~åÇ`êóëí~ääçÖê~éÜó çÑ aÉåëÉ k~kÄl P Éê~ãáÅë ïáíÜ räíê~cáåÉ dê~áå páòÉ The present study reports on the preparation and structural characterization of dense NaNbO 3 ceramics with ultrafine grain size. Nanocrystalline raw powders obtained via microemulsion mediated synthesis were consolidated to green compacts, sinterforged to ceramic pellets with high density and ultra-fine microstructure and finally annealed under different thermal regimes in order to systematically increase the average grain size in the range from several hundreds of nm up to a few mm. Structural characterization of these materials included electron-microscopic observation and X-ray diffraction in combination with temperature tuning Raman-spectroscopy in order to detect both the global and local crystallographic symmetry in dependence of the grain size. The results show that ceramics with an average grain size from approximately 360 nm to 1-2 mm consist of a phase mixture of the anti-ferroelectric phase with the space group Pbcm, which is also observed for the conventional case of coarse NaNbO 3 , and secondly of a new polar polymorph described by the space group Pmc2 1 . The volume fraction of the second polar modification appears to increase with decreasing grain size suggesting an enhancement of the piezoelectric response of ultra-fine grained NaNbO 3 ceramics in comparison to coarse grained material of the same composition.

Size-dependent lattice dynamics of barium titanate nanoparticles

“…The powder was then washed with acetic acid solution to remove the residual BaCO 3 and the unreacted Ba ions in solution. The removal of residual BaCO 3 is crucial because its Raman spectra appear in the range of <200 cm −1 [20]. After washing, the recovered powder was dried at 60 • C on a hot plate for 48 h.…”

Microemulsion Approach to Non‐Agglomerated and Crystalline Nanomaterials

“…[2] Based on a microemulsion approach, very different compounds with defined diameter and chemical composition are within reach. Recent work aiming at nanometer-scale ZnS, [3] LiFePO 4 , [4] AgBr, [5] SrAl 2 O 4 , [6] Fe 3 O 4 , [7] CdMoO 4 , [8] YVO 4 , [9] NiB, [10] BiOCl, [11] MnO 2 , [12] BaTiO 3 , [13] WO 3 , [14] Si, [15] TiO 2 , [16] or NaNbO 3 [17] may elucidate the potential of microemulsions concerning chemical synthesis.…”

“…This finding has been denoted to be a severe drawback of microemulsion techniques. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Another immanent restriction of microemulsion techniques is the limitation to ambient temperature. This is a result of the thermal stability of the micelles, which leads to phase separation at temperatures higher than about 80 8C.…”

“…Since much higher temperatures are quite often required to crystallize inorganic compounds, microemulsion techniques often yield amorphous products. [2,4,6,7,[12][13][14][15][16][17] This situation, on the one hand, limits the properties of the as-prepared materials. For instance high quality color pigments, transparent conductive oxides (TCOs), or luminescent materials are restricted to highly crystalline materials.…”

Ferroelectric Properties of (Na0.5K0.5)NbO3-Based Thin Films Deposited on Pt/(001)MgO Substrate by Pulsed Laser Deposition with NaNbO3Buffer Layer

“…Growing concern about environmental problems has led to the development of lead-free piezoelectric materials with high piezoelectric properties. (K 0:5 Na 0:5 )NbO 3 (KNN), [3][4][5][6][7][8][9][10][11][12] (Bi 0:5 Na 0:5 )TiO 3 (BNT), 10,[13][14][15][16] and BaTiO 3 (BT), [17][18][19] as lead-free piezoelectric materials, have been studied for their good piezoelectric properties. In 2004, Saito et al reported that (Na 0:52 K 0:44 Li 0:04 )(Nb 0:84 Ta 0:10 Sb 0:06 )O 3 (NKLNTS) in the KNN system shows excellent piezoelectric and ferroelectric properties.…”