548 Acta Chim. Slov. 2014, 61, 548–554 Kupec et al.: Study of Thermal Decomposition of (K 0.5 Na 0.5 )NbO 3 ... Scientific paper Study of Thermal Decomposition of (K 0.5 Na 0.5 )NbO 3 Thin-films Precursors with Different Amounts of Alkali-acetate Excess Alja Kupec, 1,2, * Oana Ca ˘ta ˘lina Mocioiu, 3, * Jena Cilen{ek, 1 Maria Zaharescu 3 and Barbara Mali~ 1,2 1 Jo`ef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia 2 Jo`ef Stefan International Postgraduate School, Jamova cesta 39, 1000 Ljubljana, Slovenia 3 ”Ilie Murgulescu” Institute of Physical Chemistry of Romanian Academy, 202 Splaiul Independentei, Bucharest 060021, Romania * Corresponding author: E-mail: alja.kupec@ijs.si; oana.mocioiu@gmail.com Received: 14-02-2014 Dedicated to the memory of Prof. Dr. Marija Kosec. Abstract Liquid precursors of (K 0.5 Na 0.5 )NbO 3 thin-films were prepared from alkali acetates and niobium ethoxide in 2-methox- yethanol solvent either in a stoichiometric ratio or with 5 or 10 mole % of potassium or sodium acetate excess. Fourier- transform infrared (FTIR) spectroscopy of the dried precursors confirmed the presence of acetate and hydroxyl groups. Thermal decompositions of the as-dried precursors in air occurred gradually. Between room temperature and ∼200 °C, the weight loss of a few per cent was due to the evaporation of residual solvents. The major mass loss was due to ther- mal oxidation of organic group with the major exothermic events at about 250 °C and 450 °C, almost 200 °C below the onset of the chemical decomposition of alkali acetates, indicating that a heterometallic complex was formed in solu- tion, in agreement with FTIR analysis. Both the amount and to a lesser extent the choice of alkali-acetate excess influen- ced the thermal decomposition of the organic groups predominantly in the temperature interval between ∼200 °C and ∼400 °C. Keywords: Lead-free, Alkaline Niobates, Thermal analysis, Fourier-transform infrared spectroscopy 1. Introduction Lead-free piezoelectric ceramics have been the topic of intensive research since early 2000’s due to the increased awareness of both health- and environment hazards related to fabrication, use and disposal of lead-based piezoelec- trics. 1 In addition to studies of bulk piezoelectric and ferroe- lectric ceramics, the research of thin films has been promo- ted by miniaturization trends in electronics and microelec- tromechanical systems. 2,3 Sodium potassium niobate with the alkali metal molar ratio equal to 1 (K 0.5 Na 0.5 )NbO 3 (KNN) has been one of the intensively studied lead-free materials compositions, which could replace human- and environment-hazardous lead-ba- sed perovskites. 4,5 Processing problems related to KNN films have been reported, and they are related to humidity sensitivity of reagents, ease of formation of non-perovskite phases upon heating, volatility of alkali oxides at the proces- sing temperatures, and consequent loss of stoichiometry and degraded functional properties, to name only some. 6–11 In Chemical Solution Deposition of thin films, the possible loss of alkalis upon heating could be compensated by the addition of excess of alkali compounds in the coating solution. In different studies, the latter varied from no excess (0) to 20 mole %, nevertheless, the films crystallized in pe- rovskite phase 9–11 In our previous work we prepared KNN thin films from acetate-alkoxide based solutions containing 0, 5 or 10 mole % of sodium or potassium acetate excess in