Sodium Potassium Niobate Based Piezoelectric Ceramics

Abstract

NKN doped samples, (100-x)NKN-xSBN (0 smaller or equal to x smaller or equal to 10) were produced using the conventional mixed oxide route with 0.45 wt% Fe2O3 sintering aid (xSBNF). After 20-24 hours mixing, samples were calcined at 850°C and sintered at 1100-1140°C (± 180°C/hour) for 4 hours. By XRD 4 mol% SBN was found to be the solubility limit for single phase structure. By SEM, second phases were visible when 2 smaller or equal to x smaller or equal to 4; their structure was subsequently shown to be tungsten bronze type (TBT). 2-4 SBNF samples were high density, over 96% theoretical. For x = 0, TC = 457°C, TO-T = 234°C, Pr = 22 μC/cm2 and EC = 16.5 kV/cm. TC was found to decrease by 14.7°C and TO-T by 9.0°C per 1 mol% addition SBN. 2SBNF was the optimal formulation in terms of microstructure and electrical properties, with average grain size 3 micro metre, Pr = 25 μC/cm2 and EC = 8.8 kV/cm, ρ = 4.7 kΩm and Q = 1.16 eV. This material comprised approximately 90% orthorhombic and 10% tetragonal phases coexisting. Pseudo-cubic lattice parameters are a' = c' = 3.947180 A, and b' = 3.999996 A for orthorhombic phase; the tetragonal has a' = c' = 3.989798 A, and b' = 3.975777 A.Synchrotron XRD studies were undertaken as a function of temperature on 99.5NKN-0.5CuO + 0.6 wt% Nb2O5 solid and powder samples. The data were Rietveld refined. The solid sample underwent two polymorphic phase transitions at 300°C and 515°C; the latter was between two tetragonal phases: lattice parameters for the tetragonal phase (300-520°C) were a' = c' = 4.99557 A, and b' = 4.0363 A; high temperature tetragonal (>500°C) exhibited a' = c' = 4.9519 A, and b' = 4.4941 A The powder sample of the same formulation exhibited more, smaller transformations. It was only orthorhombic at temperatures

Date of Award	1 Aug 2012
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Robert Freer (Supervisor)