A round-robin to measure the direct piezoelectric coefficient using the Berlincourt method.

An international round-robin exercise to measure the direct piezoelectric coefficient (d33) using the Berlincourt method has taken place under the auspices of the Versailles Project on Advanced Materials And Standards (VAMAS). Three material compositions, representing both “soft” and “hard” piezoceramics, at two different nominal thicknesses, 1mm and 10mm, were distributed to the participating laboratories. Each laboratory received a separate set of specimens accompanied by a set of instructions specifying the measurement requirements and a list of controls and precautions, to be followed as closely as possible, and a report template for the results. All specimens were supplied poled and electroded, and were checked for outliers before being sent to participants. The results obtained using different equipment configurations and different test parameters from those recommended showed large inter-laboratory variations; however the measurements made by following the recommendations supplied with the samples agreed well with each other. Data on the repeatability and reproducibility of the technique are presented. Conclusions for the measurement procedure are: i) using current variable practices results in very poor inter-laboratory reproducibility ~15%; ii) using current variable practices produces good repeatability <5%; iii) following a standard procedure produces excellent repeatability <1%; iv) following a standard procedure results in very good inter-laboratory reproducibility <3%; v) soft, thin materials are a notable exception with repeatability ~4% and reproducibility ~10%, but this issue has long been recognised for these materials.