Iranian Journal of Ceramic Science & Engineering
Volume 13, Issue 2 (8-2024)
2024, 13(2): 59-75 |
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Feizpour M, Barzegar Bafrooei H. A proposed approach for improving the density of KNN piezoelectric ceramics. Iranian Journal of Ceramic Science & Engineering 2024; 13 (2) :59-75
URL: http://ijcse.ir/article-1-995-en.html
URL: http://ijcse.ir/article-1-995-en.html
1- Meybod University , feizpour@gmail.com
2- Meybod University
2- Meybod University
Abstract: (301 Views)
In this study, the improvement of the density of lead-free potassium–sodium niobate piezoelectric ceramics with the composition (K0.50Na0.50)NbO3, abbreviated as KNN, has been investigated as an alternative to conventional lead-based piezoceramics. The powder, calcined twice at 625 °C, was pressed without the use of any binder or organic additive. In the sintering thermal profile, an initial adsorbed water-removal step of two hours at 200 °C was included for all sample series, and the effect of an additional five-hour pre-heating treatment at 400 °C, 600 °C, or 800 °C (individually) on the sample density under optimal sintering conditions (1100 °C for two hours) was evaluated.
Bulk density measurements (Archimedes method) of sintered ceramics at different pre-heating temperatures show that, while the density of samples sintered only with the initial adsorbed water-removal step (without additional pre-heating treatment) reached 92.2 ± 0.1 % of the theoretical KNN density, the relative densities of samples pre-heated at 400 °C, 600 °C, and 800 °C reached separately 95.0 ± 0.2 %, 95.3 ± 0.1 %, and 95.6 ± 0.2 %, respectively. The density values obtained from dimensional volume measurements exhibited a similar increasing trend. The relative dielectric constant (εᵣ) of the sample with the highest density was measured to be 351, 473, and 5276 at room temperature, 110 °C, and the Curie temperature, respectively, while the dielectric loss factor (tan δ) at the same temperatures was 0.043, 0.031, and 0.013, respectively, all measured at a frequency of 100 kHz.
The results indicate that introducing a five-hour pre-heating step at 800 °C in the sintering profile of potassium–sodium niobate piezoelectric ceramics can effectively enhance the sintered density by approximately 3 %. This three-percent increase in the density of pure, additive-free KNN is particularly significant since it was achieved without any sintering aids or advanced sintering techniques such as HP, SPS, or two-step sintering. Moreover, two mechanisms responsible for this improvement in KNN density are discussed, and the presented sintering profile is proposed as a recommended thermal regime for the sintering of KNN ceramics.
Bulk density measurements (Archimedes method) of sintered ceramics at different pre-heating temperatures show that, while the density of samples sintered only with the initial adsorbed water-removal step (without additional pre-heating treatment) reached 92.2 ± 0.1 % of the theoretical KNN density, the relative densities of samples pre-heated at 400 °C, 600 °C, and 800 °C reached separately 95.0 ± 0.2 %, 95.3 ± 0.1 %, and 95.6 ± 0.2 %, respectively. The density values obtained from dimensional volume measurements exhibited a similar increasing trend. The relative dielectric constant (εᵣ) of the sample with the highest density was measured to be 351, 473, and 5276 at room temperature, 110 °C, and the Curie temperature, respectively, while the dielectric loss factor (tan δ) at the same temperatures was 0.043, 0.031, and 0.013, respectively, all measured at a frequency of 100 kHz.
The results indicate that introducing a five-hour pre-heating step at 800 °C in the sintering profile of potassium–sodium niobate piezoelectric ceramics can effectively enhance the sintered density by approximately 3 %. This three-percent increase in the density of pure, additive-free KNN is particularly significant since it was achieved without any sintering aids or advanced sintering techniques such as HP, SPS, or two-step sintering. Moreover, two mechanisms responsible for this improvement in KNN density are discussed, and the presented sintering profile is proposed as a recommended thermal regime for the sintering of KNN ceramics.
Keywords: Piezoelectric ceramics, Potassium sodium niobate, Solid-state synthesis and sintering, Bulk density, Dielectric properties
Type of Study: Research |
Subject:
Electrical, Optical and Magnetic Ceramics
Received: 2025/10/20 | Accepted: 2026/02/9
Received: 2025/10/20 | Accepted: 2026/02/9
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