Solid-state synthesis of undoped and Sr-doped K0.5Na0.5NbO3
The solid-state synthesis of undoped K0.5Na0.5NbO3 (KNN) and KNN doped with 1, 2 and 6 mol% Sr, from potassium, sodium and strontium carbonates with niobium pentoxide, was studied using thermal analysis and in situ high-temperature X-ray diffraction (HT-XRD). The thermogravimetry and the differential thermal analyses with evolved-gas analyses showed that the carbonates, which were previously reacted with the moisture in the air to form hydrogen carbonates, partly decomposed when heated to 200 °C. In the temperature interval where the reaction was observed, i.e., between 200 and 750 °C, all the samples exhibited the main mass loss in two steps. The first step starts at around 400 °C and finishes at 540 °C, and the second step has an onset at 540 °C and finishes with the end of the reaction between 630 and 675 °C, depending on the particle size distribution of the Nb2O5 precursor. According to the HT-XRD analysis, the perovskite phase is formed at 450 °C for all the samples, regardless of the Sr content. The formation of a polyniobate phase with a tetragonal tungsten bronze structure was detected by HT-XRD in the KNN with the largest amount of Sr dopant, i.e., 6 mol% of Sr, at 600 °C.
KeywordsPotassium sodium niobate Solid-state synthesis Thermal analysis High-temperature X-ray diffraction
This work was supported by the Slovenian Research Agency, under Grants P2-0105 and PR-03727. The authors would like to thank Edi Kranjc for measuring the HT-XRD of the samples.
- 1.Acmite Market Intelligence. Global piezoelectric device market, market report. Ratingen: Acmite Market Intelligence; 2014.Google Scholar
- 2.EU-Directive 2002/96/EC. Waste electrical and electronic equipment (WEEE). Off J Eur Union. 2003;46(L37):24–38.Google Scholar
- 3.EU-Directive 2002/95/EC. Restriction of the use of certain hazardous substances in electrical and electronic equipment (RoHS). Off J Eur Union. 2003;46(L37):19–23.Google Scholar
- 6.Safari A, Akdogan EK, editors. Piezoelectric and acoustic materials for transducer applications. New York: Springer; 2008.Google Scholar
- 9.Jaffe B, Cook WR, Jaffe H. Piezoelectric ceramics. London: Academic Press; 1971.Google Scholar
- 14.Acker J, Kungl H, Hoffmann MJ. Influence of alkaline and niobium excess on sintering and microstructure of sodium-potassium niobate (K0.5 Na0.5)NbO3. J Am Ceram Soc. 2010;93(5):1270–81.Google Scholar
- 18.Hreščak J, Bencan A, Rojac T, Malič B. The influence of different niobium pentoxide precursors on the solid-state synthesis of potassium sodium niobate. J Eur Ceram Soc. 2013;33(15–16):3065–75.Google Scholar
- 19.Priya S, Nahm S, editors. Lead-free piezoelectrics. New York: Springer; 2012.Google Scholar
- 20.Malič B, Jenko D, Starowicz M, Bernard J, Kosec M, editors. Processing and characterization of (K, Na)NbO3 based piezoceramics. In: International conference on microelectronics, devices and materials, vol 38. Lipica, Slovenia: MIDEM—society for microelectronics, electronic components and materials; 2002.Google Scholar
- 21.Jenko D. Synthesis of (K, Na)NbO3 ceramics [Ph.D. thesis]. Ljubljana: University of Ljubljana; 2006.Google Scholar
- 24.Liptay G. Atlas of thermoanalytical curves. Budapest: Akademiai Kiado; 1974.Google Scholar