| Abstract [eng] |
Research on dielectric materials began in the 19th century, with the aim of understanding the analogy between the flow of current through a capacitor and the charge-discharge processes of the plates placed in the capacitor. The scientific community has begun to realize that some dielectric crystals may have other properties. Pyroelectric properties were initially discovered, followed by piezoelectric and finally ferroelectric properties. The discovery of these properties has led to the widespread application of dielectric crystals in today’s society. Depending on the application, the ferroelectric crystals must have higher (more sensitive) dielectric, pyroelectric or piezoelectric properties. For earlier mentioned features there is a related group of ferroelectrics called relaxor ferroelectrics (relaxors) that have been receiving special attention for the past decades. Pb(Zn1/3Nb2/3)O3 (PZN) together with Pb(Mg1/3Nb2/3)O3 (PMN) are so-called canonical relaxors and play a crucial role in the field of piezoelectrics and are highly suitable for ultrasonic transducers, electromechanical actuators. The main goal of our work is to investigate dielectric and electromechanical properties of (1- x)PbZn1/3Nb2/3O3-xPbTiO3 (x = 4.5 %, 6 %, 7 %, 12 %) single crystals along morphotropic phase boundary (MPB). In this work, three types of experimental measurements were performed to determine the dielectric and electromechanical properties of PZN–xPT. The dielectric spectroscopy experiments were carried in two different experimental setups. The first one was done using impedance analyzer HP Agilent 4284A in the frequency range of 20 Hz to 1000 Hz. The second setup was done by measuring complex reflection coefficient using network analyzer Agilent 8714ET/ES in 1–300 MHz frequency range. Nonlinear dielectric sensitivity measurements were used to investigate the types of phase transitions in our relaxors. The electromechanical properties of PZN-xPT single crystals were measured with the AixaCCT TF2000 complex measurement system. 58 Conclusions: 1. The results of thermal dielectric constant dependence studies showed that the single crystals PZN-xPT possesses typical features of ferroelectric relaxors: the maximum of dielectric permittivity is widespread and its position on the temperature axis depends on the frequency. Increased concentration of lead titanate results in a I type phase transition in the PZN-12PT single crystal. Nonlinear results of dielectric spectroscopy showed unusual negative peaks for relaxors. 2. Typically, the properties of canonical relaxors are determined by the existing polar nano regions. However, in the case of PZN-xPT, we have existing domains of different sizes with domain walls that affect the dielectric, polarization, and electromechanical displacement results. 3. Investigated PZN-xPT single crystals at room temperature have the polarization hysteresis loop characteristic of classical ferroelectrics. 4. PZN-6PT and PZN-7PT crystals have the highest dielectric and the most sensitive piezoelectric properties due to the uniform rotation of the polarization vector in one plane. |
