A study of electromechanical properties of PMN-PT ceramics and analysis of the effects of loss on frequency response of piezoelectric ceramics

Two areas of piezoelectric ceramic research are discussed. First, a study of structure-property relations in PMN-PT is presented. Then, results of a study of effects of various loss mechanisms in ceramic resonators are given.; Ceramic lead magnesium niobate-lead titanate ((1-x)PMN-xPT) of different compositions was prepared by the columbite precursor method. This study covers compositions ranging from 0.94PMN-0.06PT to 0.60PMN-0.40PT, focusing on two areas of the (1-x)PMN-xPT system: compositions that exhibit electrostrictive behavior and those that show piezoelectric behavior. Optimal electromechanical properties are obtained with the composition 0.82PMN-0.18PT, measured at T=T{dollar}rmsb{lcub}m{rcub}{dollar}=80{dollar}spcirc{dollar}C and with a DC bias of 5 kV/cm. Under these conditions the dielectric constant is 32000 and the planar coupling coefficient is 0.55. X-ray diffraction is used to study crystal structure of the (1-x)PMN-xPT system near the morphotrophic phase boundary (MPB). In this study, it is shown that the (1-x)PMN-xPT system has a compositionally wide two-phase region surrounding the MPB. The compositions 0.72PMN-0.28PT and 0.60PMN-0.40PT correspond to the rhombohedral and tetragonal single phase boundaries of the two-phase region, respectively, and 0.655PMN-0.345PT is the MPB composition. Electromechanical property evaluation shows that the optimal piezoelectric properties (d{dollar}sb{lcub}33{rcub}=720{dollar} pC/N, K = 5400, k{dollar}rmsb{lcub}p{rcub}{dollar} = 62%, and k{dollar}rmsb{lcub}t{rcub}{dollar} = 46%) are obtained at the MPB composition.; A review of work involving loss in ceramic resonators represented via complex material constants and equivalent circuits from past literature is presented. The concept of a complex electromechanical coupling coefficient is presented, and its connection to complex material constants is discussed. The complex electromechanical coupling coefficient results directly from the complex material constants from which it is comprised. As a consequence of the complex electromechanical coupling coefficient, complex resonance frequencies arise and are presented. This means that the natural resonance frequencies of a lossy piezoelectric material are in complex frequency space and, if stimulated near a complex frequency, will exhibit typical piezoelectric frequency response profiles.; An example, using computer simulation, is presented using the MPB composition of PMN-PT to show its complex resonance frequency and behavior when subject to excitation by complex frequencies. When excited with a complex frequency voltage source, the measured current response attains a maximum value at the natural (complex) resonance frequency.