Lead-free piezoelectrics: V3+to V5+ion conversion promoting the performances of V-doped Zinc Oxide.
Vanadium doped ZnO (VZO) thin films were grown by RF magnetron sputtering, starting from a ZnO:V ceramic target. The crystal structure, chemical composition, electric and piezoelectric properties of the films were investigated either on the as-grown thin films or after a post-deposition rapid thermal annealing (RTA) treatment performed at 600 °C for different lengths of time (1 and 5 min) in an oxygen atmosphere. Substitutional doping of Zn2+with V3+and V5+ions strongly deteriorated the hexagonal wurtzite ZnO structure of the as-grown thin films due to lattice distortion. The resulting slight amorphization led to a poor piezoelectric response and higher resistivity. After the RTA treatment, strong c-axis oriented VZO thin films were obtained, together with a partial conversion of the starting V3+ions into V5+. The improvement of the crystal structure and the stronger polarity of both V3+- O and V5+- O chemical bonds, together with the corresponding easier rotation under the application of an external electric field, positively affected the piezoelectric response and increased conductivity. This was confirmed by closed-loop butterfly piezoelectric curves, by a maximum d33piezoelectric coefficient of 85 pm·V-1, and also by ferroelectric switching domains with a well-defined polarization hysteresis curve, featuring a residual polarization of 12.5 μC∙cm-2.
Center for Sustainable Future Technologies @POLITO, Istituto Italiano di Tecnologia, C.so Trento 21, 10129 Torino, Italy.|Department of Applied Science and Technology, Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Turin, Italy.
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Laurenti
Center for Sustainable Future Technologies @POLITO, Istituto Italiano di Tecnologia, C.so Trento 21, 10129 Torino, Italy.
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Castellino
Center for Sustainable Future Technologies @POLITO, Istituto Italiano di Tecnologia, C.so Trento 21, 10129 Torino, Italy.
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Perrone
Center for Sustainable Future Technologies @POLITO, Istituto Italiano di Tecnologia, C.so Trento 21, 10129 Torino, Italy.|Institute of Physics, Dagestan Scientific Center, Russian Academy of Sciences, Yaragskogo Str. 94, 367003 Makhackhala, Russia.
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Asvarov
Department of Applied Science and Technology, Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Turin, Italy.
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Canavese
Center for Sustainable Future Technologies @POLITO, Istituto Italiano di Tecnologia, C.so Trento 21, 10129 Torino, Italy.
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Chiolerio