Detailed study of the phase compositions and temperature dependent properties at the morphotropic phase boundary in alkaline niobate based piezoelectric ceramics
Zusammenfassung der Projektergebnisse
High‐throughput experimentation is a very good tool to investigate the properties of a large amount of samples in order to identify the compositions with interesting properties. A precondition for the success of this process is that all the steps involved in the synthesis and characterization of the samples should be high‐throughput compatible. In this project overall, the main bottlenecks of our HTE process were that some of the characterisation tools were not through‐put compatible, low resolution of the laboratory X‐ray diffraction and lack of adequate trained manpower. It turned out that the HTE method is best suited only for screening of samples while the conventional ceramic processing method is better to determine the exact properties of the ceramics. The main outcomes of the HTE experimentation in this project are: New phase boundaries were discovered using X‐ray diffraction at room temperature but they did not translate into very high piezoelectric properties as previously thought. The phase transition temperatures in our work correspond very well with the published results for KNN ceramics while phase stability over a wide temperature range is obtained with Li and Ta co‐doping. The apparent density values of the samples are 2‐3% less when compared to values for similar compositions in the literature. The reproducibility of the density values were however relatively good. Moderately high dielectric constant values and high dielectric loss values were obtained for the samples. Compared to literature values, the dielectric constants were between 10‐20% less while the loss values were an order of magnitude higher. The resistivity values of the samples are quite good for the well sintered samples but compared to results for similar compositions, the values are about one order of magnitude lower. The analysis of the effect of density on the dielectric properties values show that density had little effect on the dielectric constant but the piezoelectric coefficients values of the samples sharply decreases. For samples with low density values, the piezoelectric coefficient values were very low. The d*33 values for relatively dense samples with K content between 60 and 80 mol% were relatively good but were 10‐20 % lower when compared to samples with similar compositions in the literature. KNN ceramics with Li and Ta amounts >5 mol% and ≥ 15mol% respectively at room temperature in both the tetragonal and mixed tetragonal‐orthorhombic phases show temperature stability of the phases. The increasing amount of K in KNN ceramics stabilizes the orthorhombic phase while increasing amounts of Li and Ta increases the tendency to form the tetragonal phase. The samples in this composition range with high K amounts show the best piezoelectric d*33 values which ranges from 200 pm/V to 250 pm/V. When these values are compared to the d*33 values reported by Saito et al. 2 for similar compositions, the obtained values are relatively good. The lowering of the tetragonal to orthorhombic phase transition temperatures to around room temperatures is believed to be one of the reasons for the increase in piezoelectric charge coefficient values. The doping of KNN‐based ceramics with Mn improves the sintering behavior of the samples. When small amounts of Mn (<2 mol%) is used, the dielectric constant value increases and the dielectric loss value is lowered. When large amounts of Mn (>2 mol%) is used, high dielectric constant values are obtained but the dielectric loss values are also high. The ferroelectric properties and piezoelectric coefficients decrease with increasing amount of Mn present. A new monoclinic phase with P11m space group is observed when KNN ceramics modified with Li is doped with 2 mol% Mn.
Projektbezogene Publikationen (Auswahl)
- “Electrical and structural characterization of (KxNa1‐x)NbO3 ceramics modified with Li and Ta”, J. Appl. Cryst. (2011), 44, 1080‐1089
H. E. Mgbemere, M. Hinterstein, G. A. Schneider
- Investigation of fracture toughness of modified (KxNa1−x)NbO3 lead‐free piezoelectric ceramics, Journal of the European Ceramic Society 32 (2012) 3339–3344
E. D. Yilmaz, H. E. Mgbemere, H. Özcoban, R. P. Fernandes, G. A. Schneider
(Siehe online unter https://doi.org/10.1016/j.jeurceramsoc.2012.04.005) - “Investigation of the structure and properties of (KxNa1‐x)NbO3‐ based piezoelectric ceramics using both conventional and high‐throughput experimentation (HTE) methods”, PhD thesis, Cuvillier Verlag Göttingen, 2012
H. E. Mgbemere
- “Structural phase transitions and electrical properties of (KxNa1‐x)NbO3‐based ceramics modified with Mn”, J. Eur. Ceram. Soc., 32(16) (2012) 4341‐4352
H. E. Mgbemere, M. Hinterstein, G. A. Schneider
(Siehe online unter https://doi.org/10.1016/j.jeurceramsoc.2012.07.033) - “Investigation of the structure and electrical properties of (KxNa0.96‐xLi0.04)(Nb0.96‐yTaySb0.04)O3 piezoelectric ceramics modified with Manganese”, J. Am. Ceram. Soc., 96[1] 201–208 (2013)
H. E. Mgbemere, M. Hinterstein, G. A. Schneider
(Siehe online unter https://doi.org/10.1111/jace.12019)
