Electrical and mechanical properties of smart PNN-PT ceramic materials

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Electrical and mechanical properties of smart PNN-PT ceramic materials


Author: Wang, Song
Title: Electrical and mechanical properties of smart PNN-PT ceramic materials
Degree: M.Sc.
Year: 2009
Subject: Hong Kong Polytechnic University -- Dissertations
Ceramic materials -- Electric properties
Ceramic materials -- Mechanical properties
Department: Dept. of Mechanical Engineering
Pages: 137 leaves : ill. ; 30 cm.
InnoPac Record: http://library.polyu.edu.hk/record=b2353053
URI: http://theses.lib.polyu.edu.hk/handle/200/5657
Abstract: The lead-based ferroelectric lead nicke1 niobate-Lead titanate (PNN-PT) with nominal composition O.64PNN-0.36PT (abbreviated as PNN-PT) is studied in this project. This composition of PNN-PT with around 36 mol% PT is at its morphotrophic phase boundary (MPB) region where it has very high dielectric and piezoelectric properties. In this project, two types of samples were fabricated. PNN-PT powders were prepared by glycerol-assisted solid state reaction route, and conventional solid state reaction method was also employed to fabricate the powders for comparison. PNN-PT ceramic discs were fabricated using the dry pressing and sintering method. The dielectric and piezoelectric properties of the ceramics were measured. XRD results reveal that the pure perovskite structure was achieved in PNN-PT powders synthesized via the glycerol-assisted route. In contrast, the undesired pyrochlore phases still remained in PNN-PT calcined powders prepared by the conventional solid state reaction method. The properties measurement shows that PNN-PT ceramics prepared by glycerol-assisted route exhibit better electric performance, compared with the ceramics prepared by conventional so1id state reaction method. For ceramics prepared via glycerol-assisted route, the relative dielectric constant ε and piezoelectric constant d₃₃are 6028 and 500x10-¹ ² C/N, respectively. The thennal analysis results demonstrate that the interaction between glycerol and PbO has altered the temperatures for phase fonnation and crystallization. The SEM images show that PNNT -glycerol ceramics exhibit much denser structure than that of PNNT ceramics. This is consistent with the result of density measurement. The measured density of PNN-PT ceramics prepared via glycerol-assisted route is 7.75 g/cm³ Besides, the SEM images show that glycerol-assisted PNNT ceramics exhibits good perfonnance under an alternating electric field. The microhardness values of PNNT and PNNT-glycerol ceramics are very close to each other, and the value of the former is slightly higher than that of the latter. The flexural test result indicates that the flexural strength of the PNNT ceramics is slightly higher than PNNT-glycerol ceramics.

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