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Relaxor-PbTiO3 single crystals and polycrystals: processing, growth and characterisation

Stoica, Laura Andreea (2016) Relaxor-PbTiO3 single crystals and polycrystals: processing, growth and characterisation. PhD thesis, University of Leeds.

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Abstract

Acoustic transducers operate using polycrystalline lead zirconate titanate (PZT) since the 1950s’. Recently, relaxor-lead titanate (relaxor-PT) single crystals have been developed and exhibit up to 650% higher piezoelectric charge coefficient and up to 50% higher electromechanical coupling factor, compared with PZT. Transducers built with relaxor-PT crystals show increased bandwidth, lower power consumption and increased sensitivity. Despite the significant advantages over PZT, a growth method for relaxor-PT single crystals that is both economical and able to produce homogeneous, highly dense crystals is yet to be found. Furthermore, one of the most important relaxor-PT solid solution is Mn modified Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3- PbTiO3 due to its thermal stability and low electrical and mechanical losses compared with other relaxor-PT solid solutions. However, the behaviour of Mn in this compound is not fully understood and control of properties, such as the mechanical quality factor, is difficult. The aim of this study was to compare Bridgman and Solid State techniques for growth of single crystalline Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3. Subsequent to this, several Mn modified compositions were designed and investigated to determine the mechanisms by which mechanical and electrical losses are lowered upon Mn incorporation. Bridgman experiments have shown that a 20 mm ø x 60 mm length and highly dense single crystal can be obtained, with (011) the natural growth direction. Seeded Bridgman was also investigated as a method of controlling the orientation of the grown crystal, but was proven challenging due to nucleation of several crystallites. Solid State experiments, which involve attaching a single crystal seed to a polycrystalline matrix and promoting boundary migration of the seed into the matrix, showed that crystal growth is encouraged when a Pb-based interlayer exists in between the seed and matrix. An epitaxially deposited, uniform thin film as interlayer was found particularly beneficial. More research is needed to determine conditions for growth of a single crystal of useful size by Solid State. Analysis of several relaxorPT compositions modified with the same amount of Mn revealed that alterations of the relaxor-PT formulation affects behaviour of the multi-valent Mn which in turn in- fluences electromechanical properties. These findings are of use to the industrial and scientific communities. Crystal growth results indicate Bridgman as suitable method if growth of crystals is desired in a short time frame, whilst Solid State results provide the basis of a new approach for growing relaxor-PT crystals. The study of Mn modified compositions provides new insights into the role of Mn substitution for manipulating the electrical and mechanical properties of complex, relaxor-PT solid solutions.

Item Type: Thesis (PhD)
Keywords: piezoelectric, ferroelectric, single crystals, polycrytstal, ceramics, solid solution, relaxor, lead titanate, Bridgman, Solid State Conversion Growth, manganese
Academic Units: The University of Leeds > Faculty of Engineering (Leeds) > School of Chemical and Process Engineering (Leeds) > Institute for Materials Research (Leeds)
Identification Number/EthosID: uk.bl.ethos.703356
Depositing User: Dr Laura A Stoica
Date Deposited: 14 Feb 2017 14:59
Last Modified: 25 Jul 2018 09:54
URI: http://etheses.whiterose.ac.uk/id/eprint/16259

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