Combined Analytical Transmission Electron Microscopy Approach to Reliable Composition Evaluation of KTaO3

Abstract

We have made an effort to obtain a reliable quantitative composition of KTaO3, which belongs to the group of incipient ferroelectrics. A combination of two analytical spectroscopic methods of transmission electron microscopy was employed for the nanoscale analysis: energy‐dispersive X‐ray and electron energy‐loss spectroscopy. Because of the volatile nature of alkali‐based compounds, special attention was paid to optimization of acquisition parameters. The latter were tested on KTaO3 single‐crystal specimen by applying various electron doses and monitoring the K/Ta ratio. The case study was based on the analysis of calcined KTaO3 powder prepared from a stoichiometric mixture of K2CO3 and Ta2O5, and KTaO3 ceramic prepared from the latter powder by hot pressing. At nanoscale, the particles of microscopically homogeneous powder appeared to have a slight excess of K relative to the nominal composition. Additionally, 5–20 nm sized nanoparticles, possessing both K‐ and Ta‐rich compositions, were found to be attached to the cubic‐shaped powder particles. Hot‐pressed KTaO3 ceramic revealed exaggerated grain growth with compositional deviations of up to 5% within large grains as well as in matrix grains composition. The majority of analyzed matrix grains, however, showed a slight excess of Ta relative to the nominal composition.

Using Infrared Spectroscopy to Identify New Amorphous Phases - A Case Study of Carbonato Complex Formed by Mechanochemical Processing

“…Mechanochemical processing has recently provided important improvements in the synthesis of ceramic materials in the family of alkaline niobates tantalates, a rich group of materials exhibiting wide applicability; this includes KTaO 3 and (K,Na,Li)(Nb,Ta)O 3 (KNLNT), which are considered as promising materials for dielectric (microwave) and piezoelectric applications, respectively (Glinsek et al, 2011;Tchernychova et al, 2011;Rojac et al, 2008aRojac et al, , 2010. Since alkali carbonates are the most frequently used as starting alkali compounds, it naturally became of interest to understand in more details the mechanochemical reaction mechanisms in which carbonate ions (CO 3 2-) are involved.…”

Approaches for a Reliable Compositional Analysis of Alkaline-Based Lead-Free Perovskite Ceramics Using Microanalytical Methods

“…In recent publications, special attention was paid to¯nding the proper experimental conditions, where the initial material composition is preserved throughout the compositional data acquisition. 40,41 In studies of KTaO 3 , 40 a standard KTaO 3 specimen was tested for its compositional stability under electron irradiation prior to the compositional analysis. Plots of the normalized K/Ta ratio determined for three di®erent irradiation doses for both room-temperature (RT) and liquid-nitrogen-cooled (LN) measurements show similar material behavior (Figs.…”

“…An identical result was observed for the ceramic that was hot pressed for 2 h at 1250 C and 25 MPa. 40 However, during the conventional TEM analysis of the powder, the incomplete perovskite crystallization along with the existence of nanoparticles attached to the powder particles were discovered (Fig. 7(a)).…”

“…In both plots the solid line represents the nominal composition; the standard deviation of AE2 for each element is shown in dotted lines. 40 50 A. Ben can et al…”

Dense and single-phase KTaO3 ceramics obtained by spark plasma sintering

“…Unfortunately, the solid-state synthesis of alkaline ceramics is difficult because of highly hygroscopic precursors and the evaporation of potassium during conventional sintering. This leads to the nucleation of secondary phases [16][17][18][19][20] even when sintering is performed at relatively low temperature (e.g. 1598 K) [20].…”