18 results
Now showing1 - 10 of 18
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Synthesis and characterisation of dielectric composites produced from glycine and alkaline niobate-based ceramicsGlycine exhibits a little piezoelectric response when poled, while lead-free alkaline niobate-based ceramics show much higher responses. This research investigates the synthesis of a dielectric composite from a combination of glycine and (K0.45Na0.51Li0.04) (Nb0.85Ta0.1Sb0.04) O3 (KNNLST) ceramics. The mixed oxide ceramics synthesis method was used to produce the ceramics, while glycine powder was commercially procured. The composition range of the shaped and heat-treated composites is from no ceramics to 100 wt.% ceramics content. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), dielectric studies, and hysteresis measurements were used to characterize the samples. The obtained phases transformed from the monoclinic phase in glycine to a two-phase orthorhombic-tetragonal phase in the ceramics. The samples’ morphology revealed a dense microstructure with some cracks, large porosity, and smaller grain sizes. The dielectric properties showed increasing dielectric constant and loss values with increasing ceramics content, while the ac conductivity also increased with rising ceramics content. Improving the range of ceramics led to polarization hysteresis graphs indicating ferroelectricity in the samples. The properties of the composites show they can be used in electromechanical devices.Publicationtype: Journal Article12 54 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Electric-field-induced phase transition in Mn-Doped (K0.48Na0.48Li0.04)NbO3 lead-free ceramics(Göller, 2017-03-01); ; ; In situ applied-electric-field high-resolution X-ray diffraction has been used to study the field-induced response of Mn-doped (K0.48Na0.48Li0.04)NbO3 (KNN-L) ceramics produced using the conventional mixed-oxide processing route. Ferroelectric domains are observed with transmission electron microscopy with indications of nano-segregation of Mn. Rietveld refinement (FULLPROF Suite) is used to refine the diffraction patterns, and a phase change from orthorhombic symmetry with space group Amm2 to tetragonal symmetry with space group P4mm is observed when the applied field exceeds 1.4 kV/mm. Phase coexistence between the two phases is also observed at applied fields between 1.2 kV/mm and 1.3 kV/mm with possible implications of being the coercive field EC value of the sample. A better understanding of the structural behaviour of this type of lead-free ceramics will lead to improvements in their piezoelectric and electromechanical properties.Publicationtype: Journal Article86 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Effect of bismuth titanate on the properties of potassium sodium niobate-based ceramicsThe effect of modifying the properties of KNN-based ceramics with Bi2Ti2O7(BiT) been investigated in this work. The density measurements show that additions of BiT to the samples slightly increase the density values. Scanning electron microscope images of the samples indicate that the average sizes of the grains decrease with BiT addition while the volume of pores increase. X-ray diffraction results show that for (K0.5Na0.5)NbO3based samples, a transformation from orthorhombic to pseudo-cubic phase is observed. For both K0.48Na0.48Li0.04)(Nb0.9Ta0.1)O3and K0.48Na0.48Li0.04)(Nb0.86Ta0.1Sb0.04)O3-based compositions, the phase transition is from an orthorhombic-tetragonal coexistence to a tetragonal structure dominated phase coexistence. The dielectric constant, dielectric loss and resistivity values of the samples increase slightly with BiT addition. Good hysteresis curves are obtained in (K0.5Na0.5)NbO3-based samples only at low BiT amounts. Remnant polarization values between 9 μC/cm2and 25 μC/cm2are obtained for K0.48Na0.48Li0.04)(Nb0.9Ta0.1)O3and K0.48Na0.48Li0.04)(Nb0.86Ta0.1Sb0.04)O3-based samples. With the exception of KNNLT samples where the d*33values increase from 203 ± 7 pm/V at 0 mol% to 275 ± 6 pm/V at 0.35 mol%, the d*33values of the samples gradually decrease with increasing BiT content. This work shows that to obtain good properties for KNN-based ceramics, only very small amounts of BiT are required.Publicationtype: Journal ArticleScopus© Citations 6 288 379 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Investigation of the fracture toughness and electrical properties of (K, Na, Li) (Nb, Ta, Sb)O<inf>3</inf> ceramicsLead-free ferroelectric ceramics with 2 different compositions were produced using the mixed-oxide synthesis route. The electro-mechanical properties of samples doped with potassium sodium niobate (KNN) compositions of (K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3 and (K0.43Na0.53Li0.04)(Nb0.84Ta0.10Sb0.06)O3 were characterized using the single edge V-notch beam method of fracture toughness determination and hysteresis measurements. Compositional analysis using X-ray fluorescence showed similar elemental amounts between the expected and actual values. From the controlled crack growth of notched bars in four-point bending, the fracture toughness was found to be 1.13±0.11 MPa m1/2 for composition 1 and 0.92±0.12 MPa m1/2 for composition 2. The calculated high signal piezoelectric charge coefficient d′33 values for composition 1 is 470±38 pm/V and is 397±30 pm/V for composition 2. The remnant strain varied between both compositions from 0.0003 to 0.0019. The results show that slight modifications in the amounts of the same elements in a ferroelectric ceramic have very little effect on the properties.Publicationtype: Journal Article64 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Effect of La and Mn on the properties of alkaline niobate-based piezoelectric ceramicsLead-free ferroelectric (K0.44Na0.52Li0.04)(Nb0.86Ta0.1Sb0.04)O3ceramics co-doped with different amounts of both La and Mn have been produced using solid-state synthesis method. The relative density values of the unmodified sample are between 92 and 96% and decreases to ~91% for the sample with 1 mol% of the co-doping. Bi-modal grain distribution is observed in the samples while the average grain size decreases with co-doping due to grain growth inhibition by pinning of the grain boundary movement. The diffraction patterns show a transformation from an orthorhombic phase to a pseudo-tetragonal phase with co-dopants addition. The Curie temperature and the tetragonal-orthorhombic transition temperatures are lowered from ~9000 at 330 °C without modification to ~4000 at temperatures below 250 °C with co-dopant addition. The dielectric loss values of the samples also decrease from ~0.4 to 0.05 for temperatures up to 250 °C with co-doping. The remnant polarisation Prof the samples decreases from ~8.55 kV/cm to ~6.57 kV/cm with co-dopant addition. The piezoelectric charge coefficient (d33), including the normalised strain values, also decrease from ~400 pm/V and 220 pC/N to 157 pm/V and 159 pC/N, respectively with co-dopants up to 1 mol%.Publicationtype: Journal ArticleScopus© Citations 2 231 429 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Neutron diffraction study of (KₓNaₓ)NbO₃-based ceramics from low to high temperaturesA neutron diffraction study of (KxNa1-x)NbO3-based ceramics has been carried out from 5 K to high temperatures well above the Curie temperature. The diffraction data were analysed using Rietveld refinement. For pure KNN samples, especially at the Na-rich side of the phase diagram, the lowtemperature structure of simple rhombohedral symmetry changes to a highly complex monoclinic structure at a higher temperature. Chemical analysis on the samples showed good agreement of the expected and actual compositions. Trigonal, monoclinic, orthorhombic, tetragonal and cubic phase models as well as two-phase mixtures are observed depending on the temperature of measurement. Space groups R3c, P1m1, P11m, Amm2, P4mm, Pm3m and their combinations are used to refine the trigonal, monoclinic, orthorhombic, tetragonal, cubic and mixed phases, respectively. For the (K0.48Na0.48Li0.04)- (Nb0.86Ta0.1Sb0.04)O3 sample at temperatures between 5 and 300 K, the monoclinic P11m space group gives the best refinement fit. For the (K0.17Na0.83)NbO3 sample, a two-phase refinement using the trigonal R3c and monoclinic Pm space groups gave the best fit at 300 K, while at 5-150 K the trigonal R3c space group gives the best fit. The understanding of the structure of these lead-free ceramics will help in the optimization of their piezoelectric properties.Publicationtype: Journal Article53 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Investigation of the phase space in lead-free (K x Na1-x )1-y Li y (Nb1-z Ta z )O3 ferroelectric ceramicsA library of ceramic compounds based on the lead-free (KxNa1−x)1−yLiy(Nb1−zTaz)O3 solid solution has been synthesized and characterized using high-throughput experimentation (HTE) method. The phase space previously reported by Saito and Takao has been expanded to x, 0.1, 1.0, y, 0, 0.1, z, 0, 0.2, and new phase boundaries are observed. The relative density values show that with the appropriate sintering temperature, ∼92% of the theoretical density can be reached. The relative permittivity values show that with increasing amount of K+ and Ta5+, the dielectric constant values increase. The effect of density on the dielectric constant values is however minimal. Resistivity values ranging from 109 to 1013 Ω·cm are obtained for the samples. The piezoelectric charge coefficient values for selected compositions show that higher values are obtained close to the phase boundaries rather than away from them. The properties for the ceramic library using the HTE method are generally 15%–20% less than from the conventional method. This method is therefore more suited for screening of sample compositions than for producing samples with high piezoelectric properties.Publicationtype: Journal ArticleScopus© Citations 6 251 196 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Effect of Ti on the properties of (KxNa1-x)NbO3 based lead-free ceramicsThe effect of modifying lead-free alkaline niobate based piezoelectric ceramics with different amounts of Ti has been investigated. Thermal studies using a dilatometer show that increasing Ti amount leads to decreasing sintering temperature by approximately 11.7 °C for every 1 mol% of the dopant added. Chemical analysis on the ceramics reveals that the measured amounts of the alkali elements are slightly lower while small amounts of Zr were introduced to the ceramic through the milling process. Microstructural analysis shows that that the average grain size decreases with increasing dopant amount and that new, smaller sized grains are formed in the presence of Ti. Two-phase orthorhombic-tetragonal diffraction patterns are observed using synchrotron X-ray diffraction while the analysis using Rietveld refinement shows that the fraction of the tetragonal phase in the two-phase patterns increase with increasing Ti content. The dielectric, piezoelectric coefficient values and ferroelectric properties of the ceramics decrease with increasing Ti amount. The current density values in the samples increase by up to 5 orders of magnitude when more than 0.5 mol% of the dopant is added.Publicationtype: Journal Article116 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Structure and electrical properties of 0.85(Bi0.5Na0.5)TiO3-0.12BaTiO3-0.03SrTiO3 ferroelectric ceramicsThe crystal structure, domain structure and the electrical properties of 0.85(Bi0.5Na0.5)TiO3-0.12BaTiO3-0.03SrTiO3 ceramics have been investigated. Rietveld refinement with Fullprof software was used to analyze the X-ray diffraction data and a two-phase coexistence between a monoclinic (Cm) phase and a tetragonal phase (P4mm) best describes the diffraction patterns from 25°C to 100°C. Results from X-ray diffraction and dielectric measurements show that the Curie temperature is between 220°C and 240°C. The domain structure shows the presence of both non-180° domain walls and 180° domain walls similar to that already observed in Pb(ZrxT1-x)O3 ceramics. The hysteresis curves show that the coercive field decreases with increasing temperature up to 100°C. The piezoelectric charge coefficient (d33*) at 25°C is 167±25pm/V and increased only slightly with temperature up to 100°C. These properties make this piezoelectric ceramic material suitable for ultrasonic transducers, sonars, hydrophones and other applications.Publicationtype: Journal Article61 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Investigation of the structure and electrical properties of (KxNa0.96-xLi0.04)(Nb0.96-yTaySb0.04) O3 piezoelectric ceramics modified with manganeseThe effect of high doping levels of manganese (Mn) on the structure and electrical properties of (KxNa1-x)NbO3 (KNN) ceramics containing Li, Ta, and Sb has been investigated. The samples were measured using synchrotron X-ray diffraction whereas Rietveld refinement with Fullprof was used to determine the structural information as a function of temperature. Temperature-dependent dielectric measurement was used to compare the phase transition temperatures. The results show that Mn decreases the temperature range of phase coexistence between the orthorhombic and tetragonal phase from ~180°C to ~120°C. The Curie temperature remained unchanged with Mn addition while the dielectric constant and dielectric loss increased with Mn addition. High amounts of Mn led to a reduction in both piezoelectric and ferroelectric properties. The remnant polarization, remnant strain, and piezoelectric coefficient values decreased from 24 μC/cm2, 0.000824, 338 ± 37 pm/V to 13 μC/cm2, 0,00014 and 208 ± 27 pm/V, respectively for the undoped and 5 mol% Mn-doped sample. © 2012 The American Ceramic Society.Publicationtype: Journal Article28