Fine grained PZT powder by using conventional PbO and ZTH as raw materials 0.125% 0.50% Doping of PZT ceramics : T S = 900°C T S = 1050°C 1 μm Effective donor content: 1 μm 1 μm mol% 0.125 V V content donor eff. V 0.5 1La : donor) - site - (A La 0.375V 0.75Fe : aceptor) - site - (B Fe O Pb Pb 3 O 3 = - ′ ′ = ′ ′ = = • • + • • + SEM 600nm Calcined PZT powder nm 20 1 d BET 50, ≈ TEM 100nm nm 5 d BET 50, ≈ Zirconia Titania Hydrate Auer, et al., United States Patent Pub. No.: US 2009/0060831 A1 sieving calcination shaping sintering ZTH PbO attrition milling Dopants Effective donor content Synthesis and microstructure Grain Size Effects on the Electromechanical Properties of donor-doped PZT-Ceramics G. Picht 1,2 , W. Rheinheimer 2 , M. J. Hoffmann 2 1 Robert Bosch GmbH, Stuttgart, Germany, 2 Ceramics in Mechanical Engineering, Institute of Applied Materials, Karlsruhe Institute of Technology, Karlsruhe, Germany Piezoelectric ceramics of the solid solution PbZr 1-x Ti x O 3 (PZT) are state of the art materials in sensor applications such as accelerometers and ultrasonic sensors. It is known from literature that their electromechanical properties are grain size dependent. The current study analysed the grain size effect for different Zr/Ti-ratios and different donor concentrations. Dense ceramics with a grain size between 0.3 – 10.0 µm were obtained by varying the sintering temperature from 875°C to 1250°C. Hereby the Ti content was varied between 45 to 52 mol% with a fixed concentration of 1 mol% La as dopant. In a second step the Ti content was fixed at 47 mol% and the doping content was varied from 1 mol% La to co-doping with 1 mol% La and 0.75 mol% Fe. While decreasing the grain size of the material a critical size was found, at which the domain structure changes significant from complex 3-D structures to simple lamellar patterns. This is in correlation with a suppression of the distortion of the perovskite lattice below the critical grain size as shown by XRD and Raman experiments. Small and large signal dielectric and piezoelectric properties show changes in non-180° domain switching as well as changes of the intrinsic piezoelectric properties by decreasing the grain size. It is demonstrated that the critical grain size is mostly related to the amount of donor dopant. PFM analysis of the domain structure in plane in plane 500nm Change from complex domain structure to a simple lamellar domain structure by decreasing grain size. PZT 53/47 Effective donor concentration: 0.5 mol%. Topography In plane Grain size: 7-12μm (conventional preparation) 5 μm 1μm Topography In plane Large grained sample Small grained sample Grain size: 0.89 μm 500nm PZT 53/47 Effective donor concentration: 0.5 mol%. Grain size: 2.2 μm Grain size: 0.52 μm Electromechanical properties Bipolar strain hysteresis Unipolar hysteresis PZT 53/47 Effective donor concentration: 0.5 mol%. Decreasing the grain size of the PZT ceramics below a critical value leads to larger coercive fields and lower remanent strain. Both extrinsic and intrinsic contributions drop down at very low grain sizes. Influence of grain size on intrinsic and extrinsic contributions General trend of the grain size effect on the large field strain for different donor concentrations The critical grain size is strongly influenced by the amount of effective donor dopant. 1.00 0.25 0.125 0.50 PZT 53/47 Effective donor concentration: Critical grain size Critical grain size Tsurumi, Appl. Phys. Let. 2010 Grain size: 1.7 μm Grain size: 0.37 μm Decrease in tetragonal phase content and c/a-ratio by decreasing the grain size. Lattice parameter Distance from the center of the domain Cubic Tetragonal Gradient layer c 1 a 1 c 2 a 2 a 3 Zr 4+ , Ti 4+ O 2- [001] [100] Pb 2+ Critical grain size PZT 53/47 Effective donor concentration: 0.5 mol%. (200) Reflex group 1.70 μm 1.25 μm 0.52 μm 0.37 μm Grain size: Crystal structure PZT 52/48 Effective donor concentration: 0.5 mol%. The difference in the slope in the range between 10 1 - 10 8 Hz is probably caused by a different domain wall contribution to the permittivity. This implies a higher degree of disorder in the small grained sample. The relaxation frequency is influenced by the domain size and is therefore shifted towards higher frequencies by decreasing grain size. Acknowledgement: Dragan Damjanovic, Li Jin, EPFL Lausanne Frequency dispersion of the permittivity Conclusions A decrease in the grain size leads to a change in the complexity of the domain structure. The performed x-ray analysis shows a decreasing c/a-ratio for smaller grain sizes. This can be explained by an increase of the domain wall density and the pseudocubic structure close to the domain walls. This is in agreement with the frequency dependence of the permittivity showing a larger slope for a small grain size which implies a more disordered structure. The change in the domain structure and lattice parameter cause a decrease in the electromechanical properties. Below a critical grain size the intrinsic and extrinsic contributions are strongly reduced. The critical grain size is affected by the effective donor content. Motivation, Methods and Objectives 1 μm 1 μm 1 μm Control of the grain size by sintering parameters and effective donor content.