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  5. Investigating the Solid-state Phase Formation Mechanisms of Lead-free Piezoceramics using High-temperature XRD

Investigating the Solid-state Phase Formation Mechanisms of Lead-free Piezoceramics using High-temperature XRD

Piezoceramics are materials that accumulate an electrical charge in response to applied mechanical stress, or produce strain in response to applied electrical fields. They are used in areas such as sensor technology or as transducers. Since most piezoceramics are based on harmful lead, the development of lead-free alternatives is of significant interest. Non-ambient XRD can be used to characterize the phases present during the formation of these materials.

Introduction

Barium titanate (BT) was the first ferroelectric oxide to be discovered and has recently re-gained the interest of the scientific community as a baseline for the development of alternatives to lead-based piezoceramics such as PZT (lead zirconium titanate), which are used in many applications such as actuators, ultrasonic transducers, and sensors. One particularly promising lead-free material derived from BT through isovalent substitution is the (Ba,Ca)(Zr,Ti)O3 system (BCZT) which has been found to exhibit outstanding electromechanical properties and was first described in 2009 by Liu and Ren. (1,2) This discovery triggered extensive research on the system, which mostly focused on the functional properties, while less is known about the reactions happening during the solid-state synthesis process. A few sources report a limited solubility of calcium titanate in the main perovskite matrix and the presence of polytitanate secondary phases (3,4).
This study aims to determine the underlying formation reactions and identify the origin of secondary phases by X-ray diffraction (XRD). A big challenge for the realization of this task is the high processing temperatures of up to 1300 °C, which are needed for the thermal activation of the diffusion-controlled reactions in powder mixtures. This necessitated the use of a non-ambient XRD attachment that can withstand extraordinarily high temperatures.

 

References:

  1. Liu, W., & Ren, X., Physical Review Letters 2009, 103.
  2. Acosta, M., Novak, N., Rojas, V., Patel, S., Vaish, R., Koruza, J., Rossetti, G. A., & Rödel, J., Applied Physics Reviews 2017, 4.
  3. Hennings, D., & Schreinemacher, H., Materials Research Bulletin 1977, 12, 1221–1226.
  4. Jain, T. A., Fung, K., & Chan, J., Journal of Alloys and Compounds 2009, 468, 370–374.

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