Comparison of (K0.5Na0.5)NbO3 Single Crystals Grown by Seed-Free and Seeded Solid-State Single Crystal Growth

Abstract

(K0.5Na0.5)NbO3-based piezoelectric ceramics are of interest as a lead-free replacement for Pb(Zr,Ti)O3. In recent years, single crystals of (K0.5Na0.5)NbO3 with improved properties have been grown by the seed-free solid-state crystal growth method, in which the base composition is doped with a specific amount of donor dopant, inducing a few grains to grow abnormally large and form single crystals. Our laboratory experienced difficulty obtaining repeatable single crystal growth using this method. To try and overcome this problem, single crystals of 0.985(K0.5Na0.5)NbO3-0.015Ba1.05Nb0.77O3 and 0.985(K0.5Na0.5)NbO3-0.015Ba(Cu0.13Nb0.66)O3 were grown both by seed-free solid-state crystal growth and by seeded solid-state crystal growth using [001] and [110]-oriented KTaO3 seed crystals. X-ray diffraction was carried out on the bulk samples to confirm that single-crystal growth had taken place. Scanning electron microscopy was used to study sample microstructure. Chemical analysis was carried out using electron-probe microanalysis. The single crystal growth behaviour is explained using the mixed control mechanism of grain growth. Single crystals of (K0.5Na0.5)NbO3 could be grown by both seed-free and seeded solid-state crystal growth. Use of Ba(Cu0.13Nb0.66)O3 allowed a significant reduction in porosity in the single crystals. For both compositions, single crystal growth on [001]-oriented KTaO3 seed crystals was more extensive than previously reported in the literature. Large (~8 mm) and relatively dense (<8% porosity) single crystals of 0.985(K0.5Na0.5)NbO3-0.015Ba(Cu0.13Nb0.66)O3 can be grown using a [001]-oriented KTaO3 seed crystal. However, the problem of repeatable single crystal growth remains.

0.98(K0.5Na0.5)NbO3–0.02(Bi0.5Na0.5)(Zr0.85Sn0.15)O3 Single Crystals Grown by the Seed-Free Solid-State Crystal Growth Method and Their Characterization

“…However, it can be seen that the amounts of alkali cations were reduced during sintering compared to the nominal composition, and the loss was higher for K compared to Na in both the single crystal and matrix. This alkali volatilization was also observed during calcination and sintering of (K 0.5 Na 0.5 )NbO 3 -based ceramics or single crystals [41,49]. The higher K loss is due to its higher partial pressure compared to Na [22].…”

“…The size of the single crystals may be improved by choice and optimization of different sintering additives, as carried out for KNN [32,72,73]. In recent work in our laboratory, it has been found that use of a Ba(Cu 0.13 Nb 0.66 )O 3 additive and a [001]-oriented KTaO 3 seed crystal allowed growth of a large and dense single crystal of (K 0.5 Na 0.5 )NbO 3 , although problems with repeatability persisted [49]. Figure S6 shows an SEM micrograph of a 98KNN-2BNZS single crystal (with the addition of 0.15 mol% Li 2 CO 3 and 0.15 mol% Bi 2 O 3 sintering aids as before) grown at 1150 • C for 20 h using a [001]-oriented KTaO 3 seed crystal.…”