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Title: Sodium potassium niobate based piezoelectric ceramics
Author: Wegrzyn, Margaret
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2012
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NKN doped samples, (100-x)NKN-xSBN (0 ≤ x ≤ 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 ≤ x ≤ 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 μm, 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 Å, and b’ = 3.999996 Å for orthorhombic phase; the tetragonal has a’ = c’ = 3.989798 Å, and b’ = 3.975777 Å.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 Å, and b’ = 4.0363 Å; high temperature tetragonal (>500°C) exhibited a’ = c’ = 4.9519 Å, and b’ = 4.4941 Å. The powder sample of the same formulation exhibited more, smaller transformations. It was only orthorhombic at temperatures <140°C with a’ = c’ = 4.10680 Å, and b’ = 4.02620 Å. Above 140°C both orthorhombic and tetragonal phases were present. Another significant transformation occurred at 360°C where the structural unit cell parameters changed significantly. Parameter lengths are provided. P-E data was characterised by Pr = 19.9 μC/cm2 and EC = 13.5 kV/cm. Synchrotron X-ray diffraction analysis of 94 NKN-6LiTaO3 showed that tetragonal phase was present at 20-390°C, although an orthorhombic phase was identified at 20-200°C and again at 340-390°C just before the cubic transition temperature at 390°C. This is a new observation for NKN. A new and simple method for tape casting was developed to reduce powder wastage, enabling thick films of 50 μm to be cast. The reactive templated grain growth (RTGG) method was employed to orient 95NKN-5LiNbO3 and 94NKN-6LiNbO3 samples; CuO was utilised as a sintering aid. Pre-cursor BNN and NN template particles were produced using the molten salt synthesis (MSS) method, using a salt to oxide ratio of 1:1. Resulting NN particles were 15 μm wide and 0.5 μm thick. Eight layered 6LN + 0.4 wt% tapes produced using 10 wt% template particles resulted in 210 μm thick tapes with 67% orientation when sintered at 1150°C. Resulting properties include TC = 440ºC and TO-T = 70ºC, 25 kΩ resistance and capacitance 21.6 pF.
Supervisor: Freer, Robert Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: NKN ; piezoelectric ; electroceramics ; tape casting ; RTGG