31 results on '"Derek C. Sinclair"'
Search Results
2. Predicting the energy storage density in poly(methyl methacrylate)/methyl ammonium lead iodide composites
- Author
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Julian S. Dean, Ian M. Reaney, Derek C. Sinclair, and C. D. Kennedy
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010302 applied physics ,Permittivity ,Materials science ,Composite number ,General Physics and Astronomy ,02 engineering and technology ,Dielectric ,021001 nanoscience & nanotechnology ,01 natural sciences ,Poly(methyl methacrylate) ,Energy storage ,law.invention ,chemistry.chemical_compound ,Capacitor ,chemistry ,law ,visual_art ,Electric field ,0103 physical sciences ,visual_art.visual_art_medium ,Methyl methacrylate ,Composite material ,0210 nano-technology - Abstract
In high-energy density pulsed power capacitors, high permittivity particles are dispersed within a high breakdown strength polymer matrix. In theory, such composites should be able to achieve higher volumetric energy densities than is possible with either of the individual constituents. CH3NH3PbI3 (MALI) has a perovskite structure and may be fabricated at room temperature using a mechanosynthesis route in ethanol. In this study, MALI is used to form a dielectric composite with poly(methyl methacrylate) (PMMA) used as the matrix. Theoretical models are used to predict composite permittivity values that are compared to experimental values. Finite element modeling is used to simulate their effective permittivity and, beyond what the theoretical models can achieve, predicts their energy storage capabilities by analyzing electric field intensification. The simulations show increasing energy storage capability with penetration of MALI, but this is limited experimentally by their mixing capability.
- Published
- 2019
3. Electrical and structural characteristics of lanthanum-doped barium titanate ceramics
- Author
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Derek C. Sinclair, Finlay D. Morrison, and Anthony R. West
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Permittivity ,Materials science ,Ferroelectric ceramics ,Oxide ,Analytical chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,Mineralogy ,chemistry.chemical_compound ,Tetragonal crystal system ,chemistry ,visual_art ,Barium titanate ,visual_art.visual_art_medium ,Lanthanum ,Orthorhombic crystal system ,Ceramic - Abstract
Single phase La-doped BaTiO3 with the formula Ba1−xLaxTi1−x/4O3: 0⩽x⩽0.20 was prepared by solid state reaction of oxide mixtures at 1350 °C, 3 days, in O2. The tetragonal distortion in undoped BaTiO3 decreased with x and samples were cubic for x⩾0.05. Both the tetragonal/cubic and orthorhombic/tetragonal transition temperatures decreased with x, but at different rates, and appeared to coalesce at x∼0.08. The value of the permittivity maximum at the tetragonal/cubic phase transition in ceramic samples increased from ∼10 000 for x=0 at 130 °C to ∼25 000 for x=0.06 at ∼−9 °C. At larger x, the permittivity maximum broadened, showed “relaxor”-type frequency dependent permittivity characteristics and continued to move to lower temperatures. Samples fired in O2 were insulating and showed no signs of donor doping whereas air-fired samples were semiconducting, attributable to oxygen loss.
- Published
- 1999
4. Ba8ZnTa6O24: a high-Q microwave dielectric from a potentially diverse homologous series
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Richard M. Ibberson, T. Price, John B. Claridge, Sandra M. Moussa, Derek C. Sinclair, Simon J. Clarke, Matthew J. Rosseinsky, and D. Iddles
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Permittivity ,Materials science ,Physics and Astronomy (miscellaneous) ,Ferroelectric ceramics ,Mineralogy ,Relative permittivity ,Dielectric ,Crystal structure ,Crystallography ,visual_art ,visual_art.visual_art_medium ,Ceramic ,Temperature coefficient ,Perovskite (structure) - Abstract
The ceramic Ba8ZnTa6O24 has been synthesized in isolation and its dielectric and crystallographic properties characterized. The material affords excellent dielectric properties, with a high unloaded quality factor Qu=20 800 at 3.28 GHz, high relative permittivity er=29 and a temperature coefficient of resonant frequency τf=29.4 ppm/°C. The crystal structure adopted is complex, comprising mixed cubic and hexagonal perovskite subunits, and contains cation vacancies on the octahedral sites. A second phase with a closely related structure is identified, demonstrating the existence of a family of materials. This structural complexity offers diverse opportunities for substitutions calculated to enhance the figures of merit reported.
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- 2003
5. CaCu3Ti4O12: One-step internal barrier layer capacitor
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Finlay D. Morrison, Derek C. Sinclair, Anthony R. West, and Timothy B. Adams
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Permittivity ,Barrier layer ,chemistry.chemical_compound ,Materials science ,Physics and Astronomy (miscellaneous) ,chemistry ,Condensed matter physics ,Ferroelectric ceramics ,Calcium copper titanate ,Grain boundary ,Microstructure ,Capacitance ,Dielectric spectroscopy - Abstract
There has been much recent interest in a so-called “giant-dielectric phenomenon” displayed by an unusual cubic perovskite-type material, CaCu3Ti4O12; however, the origin of the high permittivity has been unclear [M. A. Subramanian, L. Dong, N. Duan, B. A. Reisner, and A. W. Sleight, J. Solid State Chem. 151, 323 (2000); C. C. Homes, T. Vogt, S. M. Shapiro, S. Wakimoto, and A. P. Ramirez, Science 293, 673 (2001); A. P. Ramirez, M. A. Subramanian, M. Gardel, G. Blumberg, D. Li, T. Vogt, and S. M. Shapiro, Solid State Commun. 115, 217 (2000)]. Impedance spectroscopy on CaCu3Ti4O12 ceramics demonstrates that they are electrically heterogeneous and consist of semiconducting grains with insulating grain boundaries. The giant-dielectric phenomenon is therefore attributed to a grain boundary (internal) barrier layer capacitance (IBLC) instead of an intrinsic property associated with the crystal structure. This barrier layer electrical microstructure with effective permittivity values in excess of 10 000 can be fa...
- Published
- 2002
6. Donor-doping and reduced leakage current in Nb-doped Na0.5Bi0.5TiO3
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Derek C. Sinclair, Linhao Li, Jiadong Zang, and Ming Li
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Materials science ,Physics and Astronomy (miscellaneous) ,Band gap ,Doping ,Inorganic chemistry ,Analytical chemistry ,Oxide ,Dielectric ,Thermoelectric materials ,Titanate ,chemistry.chemical_compound ,chemistry ,Electrical resistivity and conductivity ,Perovskite (structure) - Abstract
Low levels of so-called “donor-doping” in titanate-based perovskite oxides such as La for Ba, Sr, and Nb for Ti in (Ba, Sr)TiO3 can significantly reduce the resistivity of these typical (d0) dielectric materials and expand application areas to positive temperature coefficient resistors, thermoelectrics, conductive wafers as thin film substrates, and solid oxide fuel cell anode materials. Here, we show low levels of Nb-doping (≤1 at. %) on the Ti-site in the well-known lead-free piezoelectric perovskite oxide Na 0.5Bi0.5TiO3 (NBT) produces completely different behaviours whereby much higher resistivity is obtained, therefore indicating a different donor-doping (substitution) mechanism. There is a switch in conduction mechanism from oxygen-ions in undoped NBT with an activation energy (Ea) of
- Published
- 2015
7. Transformation from insulating p-type to semiconducting n-type conduction in CaCu3Ti4O12-related Na(Cu5/2Ti1/2)Ti4O12 ceramics
- Author
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Derek C. Sinclair and Ming Li
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Permittivity ,Materials science ,Electrical resistivity and conductivity ,Phase (matter) ,Ferroelectric ceramics ,Doping ,Analytical chemistry ,General Physics and Astronomy ,Sintering ,Mineralogy ,Ferroelectricity ,Solid solution - Abstract
A double doping mechanism of Na+ + ½ Ti4+ → Ca2+ + ½ Cu2+ on the general formula Ca1−xNax(Cu3−x/2Tix/2)Ti4O12 has been used to prepare a series of isostructural CaCu3Ti4O12 (CCTO)-type perovskites. A complete solid solution exists for 0 ≤ x ≤ 1 and all compositions exhibit incipient ferroelectric behaviour with higher than expected intrinsic relative permittivity. Although CCTO ceramics typically exhibit n-type semiconductivity (room temperature, RT, resistivity of ∼10–100 Ω cm), Na(Cu5/2Ti1/2)Ti4O12 (NCTO) ceramics sintered at 950 °C consist of two insulating bulk phases (RT resistivity > 1 GΩ cm), one p-type and the other n-type. With increasing sintering temperature/period, the p-type phase transforms into the n-type phase. During the transformation, the resistivity and activation energy for electrical conduction (Ea ∼ 1.0 eV) of the p-type phase remain unchanged, whereas the n-type phase becomes increasingly conductive with Ea decreasing from ∼ 0.71 to 0.11 eV with increasing sintering temperature. Th...
- Published
- 2013
8. First-principles study of intrinsic point defects in hexagonal barium titanate
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Derek C. Sinclair, James A. Dawson, Hungru Chen, and John H. Harding
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Band gap ,Binding energy ,Fermi level ,General Physics and Astronomy ,Crystallographic defect ,Molecular physics ,Condensed Matter::Materials Science ,symbols.namesake ,Crystallography ,chemistry.chemical_compound ,chemistry ,Ab initio quantum chemistry methods ,Vacancy defect ,Barium titanate ,Physics::Atomic and Molecular Clusters ,symbols ,Density functional theory ,Physics::Chemical Physics - Abstract
Density functional theory (DFT) calculations have been used to study the nature of intrinsic defects in the hexagonal polymorph of barium titanate. Defect formation energies are derived for multiple charge states, and due consideration is given to finite-size effects (elastic and electrostatic) and the band gap error in defective cells. Correct treatment of the chemical potential of atomic oxygen means that it is possible to circumvent the usual errors associated with the inaccuracy of DFT calculations on the oxygen dimer. Results confirm that both mono- and di-vacancies exist in their nominal charge states over the majority of the band gap. Oxygen vacancies are found to dominate the system in metal-rich conditions with face sharing oxygen vacancies being preferred over corner sharing oxygen vacancies. In oxygen-rich conditions, the dominant vacancy found depends on the Fermi level. Binding energies also show the preference for metal-oxygen di-vacancy formation. Calculated equilibrium concentrations of va...
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- 2012
9. Defect chemistry of Ti-doped antiferroelectric Bi0.85Nd0.15FeO3
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Sarah Karimi, Iasmi Sterianou, LiQiu Wang, Bernhard Schaffer, Ian MacLaren, Alan J. Craven, Kambiz Kalantari, Derek C. Sinclair, Shu Miao, and Ian M. Reaney
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Physics and Astronomy (miscellaneous) ,Chemistry ,Ferroelectric ceramics ,Scanning transmission electron microscopy ,Doping ,Analytical chemistry ,Ionic bonding ,Antiferroelectricity ,Mineralogy ,Ionic conductivity ,Multiferroics ,Conductivity - Abstract
Aberration corrected scanning transmission electron microscopy revealed that Bi0.85Nd0.15Fe0.9Ti0.1O3 ceramics contain coherent Nd-rich precipitates distributed throughout the perovskite lattice, implying charge compensation is obtained by the creation of VNd/// and not VBi///. At low concentrations, therefore, Ti4+ replace Fe2+ with the creation of 2/3VNd///, and at higher concentrations (when Fe2+ have been eliminated and the conductivity suppressed), Fe3+ with the creation of 1/3VNd///. The switch in ionic compensation mechanism from 2/3VNd/// at low Ti concentrations (∼1%) to 1/3VNd/// at higher concentrations (>1%) results in a decrease in the magnitude of ΔTC/Δx, as the disruption of long range anti-polar coupling declines.
- Published
- 2012
10. Structural phase transitions in Ti-doped Bi1-xNdxFeO3 ceramics
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Kambiz Kalantari, Ian M. Reaney, Jan Pokorný, Derek C. Sinclair, Paul A. Bingham, and Iasmi Sterianou
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Permittivity ,Phase transition ,Materials science ,Differential scanning calorimetry ,Ferroelectric ceramics ,Analytical chemistry ,General Physics and Astronomy ,Mineralogy ,Dielectric ,Atmospheric temperature range ,Ferroelectricity ,Thermal expansion - Abstract
Recently, it was demonstrated that donor doping with Ti on the B-site significantly reduces the conductivity in Bi0.85Nd0.15FeO3 ceramics [Kalantari et al., Adv. Funct. Mater. 21, 3737 (2011)]. In this contribution, the phase transitions as a function of Nd concentration are investigated in 3% Ti doped Bi1-xNdxFeO3 ceramics. Paraelectric (PE) to ferroelectric (FE) transitions were observed for compositions with x ≤ 0.125 which manifested themselves as peaks in permittivity. In contrast, PE to antiferroelectric (AFE) transitions for 0.15 ≤ x ≤ 0.20 gave rise to a step-like change in the permittivity with x = 0.25 exhibiting no sharp anomalies and remaining PE until room temperature. The large volume change at the PE to FE/AFE transitions, reported by Levin and co-workers [Phys. Rev. B 81, 020103 (2011)] and observed here by dilatometry, coupled with their first-order character constrain the transitions to occur uniformly throughout the material in an avalanche-like manner. Hence, the anomalies in DSC, permittivity and thermal expansion occur over a commensurately narrow temperature interval. However, despite the large volume change and eye-catching anomalies in DSC, the latent heats for the transitions in Ti-doped Bi1-xNdxFeO3 are similar to Pb(Zr,Ti)O3 (1–3 kJ/mol) with each an order of magnitude greater than BaTiO3 (∼0.2 kJ/mol). A broad frequency dependent dielectric anomaly of unknown origin in the temperature range 250–450 °C was also observed in all samples.
- Published
- 2012
11. The extrinsic origins of high permittivity and its temperature and frequency dependence in Y0.5Ca0.5MnO3 and La1.5Sr0.5NiO4 ceramics
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Ming Li and Derek C. Sinclair
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Permittivity ,Chemical substance ,Materials science ,Condensed matter physics ,Ferroelectric ceramics ,General Physics and Astronomy ,Mineralogy ,Dielectric ,Ferroelectricity ,Dielectric spectroscopy ,visual_art ,visual_art.visual_art_medium ,Multiferroics ,Ceramic - Abstract
Recently, many charge-ordered compounds containing mixed-valence transition metal ions have been considered as possible multiferroics. Theoretically it has been proposed that charge (orbital) ordering could generate “electronic ferroelectricity” in some of these compounds. Experimentally, temperature- and frequency-dependent high permittivity is commonly presented as evidence of ferroelectricity in these materials. Here, systematic impedance spectroscopy studies on Y0.5Ca0.5MnO3 and La1.5Sr0.5NiO4 ceramics reveal, however, the high permittivity and its temperature- and frequency-dependence over the ranges of 10–300 K and 10 Hz–1 MHz, respectively, are mainly associated with an extrinsic non-ohmic sample-electrode contact effect, rather than an intrinsic response. A general strategy to distinguish the intrinsic dielectric properties of these charge-ordered compounds from extrinsic contributions using impedance spectroscopy is also demonstrated.
- Published
- 2012
12. Use of Raman spectroscopy to determine the site occupancy of dopants in BaTiO3
- Author
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Derek C. Sinclair, O. P. Thakur, U. M. Pasha, L. Ben, Ian M. Reaney, and Jan Pokorný
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Diffraction ,Permittivity ,Dopant ,Chemistry ,Doping ,Analytical chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,Dielectric ,symbols.namesake ,X-ray crystallography ,symbols ,Raman spectroscopy ,Titanium - Abstract
Chemical doping is one of the major methods by which the properties of BaTiO3 are modified to induce various device characteristics. Doping strategies are generally separated into iso- and alio-valent (donors and acceptors) and into A- and B-site species within the perovskite structure. The A1g octahedral breathing mode at ∼800 cm−1 in BaTiO3 is Raman inactive for compositions with single B-site species. However, this mode becomes Raman active if more than one B-site species is present, including titanium vacancies, VT′′′′. Moreover, the relative intensity of the A1g breathing mode is qualitatively related to the concentration of the species replacing Ti in the B-site. This article illustrates some clear cases where the A1g octahedral breathing mode can be utilized to verify the site occupancy of dopants in BaTiO3 when used in conjunction with more conventional indirect methods such as x-ray diffraction (Vegard’s Law) and dielectric measurements as a function of temperature.
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- 2011
13. An atomistic study into the defect chemistry of hexagonal barium titanate
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James A. Dawson, John H. Harding, Colin L. Freeman, L.-B. Ben, and Derek C. Sinclair
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chemistry.chemical_compound ,chemistry ,Chemical physics ,Hexagonal crystal system ,Vacancy defect ,Inorganic chemistry ,Barium titanate ,Binding energy ,Doping ,Cluster (physics) ,General Physics and Astronomy ,Charge compensation ,Ion - Abstract
Using a recently established BaTiO3 potential model specifically designed for the calculation of defect energetics, atomistic simulations have been carried out on the intrinsic defect chemistry and Rare Earth (RE3+) doping of hexagonal barium titanate (h-BaTiO3). Five charge compensation schemes have been considered as well as potential cluster binding energies. The results show that ion size arguments are obeyed. In the dilute concentration limit, large RE3+ cations dope at the Ba-site via a titanium vacancy mechanism and mid sized RE3+ cations dope at the Ba and Ti sites simultaneously via a self compensation mechanism. In contrast, small RE3+ cations dope exclusively on the Ti-site via an oxygen vacancy compensation scheme. Comparisons between the hexagonal and cubic phases of BaTiO3 have also been drawn. It is suggested that Ba-site doping is less favorable and that Ti-site doping is considerably more favorable in h-BaTiO3 and that different defect configurations have a significant effect on the binding energies between such defects, leading to some mechanisms becoming more or less energetically favorable as a result.
- Published
- 2011
14. Extrinsic origins of the apparent relaxorlike behavior in CaCu3Ti4O12 ceramics at high temperatures: A cautionary tale
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Ming Li, Derek C. Sinclair, and Anthony R. West
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Permittivity ,Materials science ,Condensed matter physics ,Analytical chemistry ,General Physics and Astronomy ,Cubic crystal system ,Capacitance ,Dielectric spectroscopy ,visual_art ,visual_art.visual_art_medium ,Ceramic ,Contact impedance ,Fixed frequency ,Negative impedance converter - Abstract
Although the origins of the high effective permittivity observed in CaCu3Ti4O12 (CCTO) ceramics and single crystals at ∼100–400 K have been resolved, the relaxorlike temperature- and frequency-dependence of permittivity obtained from fixed frequency capacitance measurements at higher temperatures reported in the literature remains unexplained, especially as CCTO adopts a centrosymmetric cubic crystal structure in the range of ∼35–1273 K. Impedance spectroscopy studies reveal that this type of relaxorlike behavior is an artifact induced mainly by a nonohmic sample-electrode contact impedance. In addition, an instrument-related parasitic series inductance and resistance effect modifies the measured capacitance values as the sample resistance decreases with increasing temperature. This can lead to an underestimation of the sample capacitance and, in extreme cases, to so-called ‘negative capacitance.’ Such a relaxorlike artifact and negative capacitance behavior are not unique to CCTO and may be expected in o...
- Published
- 2011
15. Anomalous Curie temperature behavior of A-site Gd-doped BaTiO3 ceramics: The influence of strain
- Author
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Derek C. Sinclair and Liubin Ben
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inorganic chemicals ,Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Ferroelectric ceramics ,Doping ,technology, industry, and agriculture ,Analytical chemistry ,chemistry.chemical_element ,Ferroelectricity ,Ion ,chemistry ,Lattice (order) ,Vacancy defect ,Curie temperature ,lipids (amino acids, peptides, and proteins) ,human activities ,Titanium - Abstract
The influence of A-site Gd3+ doping on the c/a ratio, cell volume and Curie temperature (Tc) of ferroelectric BaTiO3 according to the titanium vacancy mechanism, viz., Ba1−xGdxTi1−x/4O3 has been investigated and compared to that of La3+-doping. The c/a ratio and cell volume of Gd-doped samples are larger than the equivalent La-doped samples and Tc decreases at a rate of only ∼8 °C/at. % for Gd3+ substitution compared to ∼24 °C/at. % for La3+ substitution. These trends are opposite to that expected based on ionic-radii and tolerance factor arguments. This anomalous behavior is attributed to an ion-size mismatch (cation variance) effect on the A-site between the Ba2+ and Gd3+ ions that induces local strain in the lattice that suppresses the reduction in the c/a ratio and cell volume, and as a consequence in the rate of decrease in Tc.
- Published
- 2011
16. Polar order and diffuse scatter in Ba(Ti1−xZrx)O3 ceramics
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Ian M. Reaney, Derek C. Sinclair, U. M. Pasha, O. P. Thakur, Shu Miao, and Jan Pokorny
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Diffraction ,Materials science ,Zone axis ,Analytical chemistry ,General Physics and Astronomy ,Dielectric ,Condensed Matter::Materials Science ,symbols.namesake ,Crystallography ,Electron diffraction ,Phase (matter) ,X-ray crystallography ,symbols ,Orthorhombic crystal system ,Raman spectroscopy - Abstract
The Ba(Ti1−xZrx)O3 (BTZ) system with x≤0.35 has been studied using a combination of x-ray diffraction, dielectric measurements, Raman spectroscopy, and electron diffraction with a view to better understand the changes in structure and correlation length of polar order as a function of composition and temperature. Careful fitting of Raman spectra has confirmed stabilization of the orthorhombic phase at room temperature in x=0.05 with mixed phase (orthorhombic and rhombohedral) present at 80 K. Raman data suggest that the rhombohedral phase is most likely to be present at low temperature for x=0.15 and 0.25 and that only short range polar order evolves in x=0.35. Interpretation of the Raman spectra is in broad agreement with the dielectric data as a function of composition and temperature. Diffuse scatter at room temperature in high order zone axis electron diffraction remains essentially identical for all compositions irrespective of structure and correlation length of polar order. The diffuse maxima are t...
- Published
- 2009
17. Origin(s) of the apparent high permittivity in CaCu3Ti4O12 ceramics: clarification on the contributions from internal barrier layer capacitor and sample-electrode contact effects
- Author
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Antonio Feteira, Mats Nygren, Anthony R. West, Derek C. Sinclair, Ming Li, and Zhijian Shen
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Barrier layer ,Permittivity ,Materials science ,Electrical resistivity and conductivity ,Electrode ,Metallurgy ,General Physics and Astronomy ,Spark plasma sintering ,Dielectric ,Composite material ,Ceramic capacitor ,Polarization (electrochemistry) - Abstract
CaCu3Ti4O12 ceramics with a range of resistivities have been prepared using both conventional sintering and spark plasma sintering. For all cases, the high effective permittivity is associated primarily with an internal barrier layer capacitor mechanism. Additional polarization associated with the electrode-sample interface may appear but its visibility depends on the grain boundary resistivity (Rgb) of the ceramic. If the Rgb is large, the electrode polarization is obscured by sample-related effects; if the Rgb is small, a separate impedance associated with the electrode polarization may be seen. Discrepancies in the literature regarding the magnitude and origin of the high effective permittivity are attributed to a combination of differences in processing conditions, electrode contact material and measuring frequency range.
- Published
- 2009
18. Investigation of high Curie temperature (1−x)BiSc1−yFeyO3–xPbTiO3 piezoelectric ceramics
- Author
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Derek C. Sinclair, Ian M. Reaney, Iasmi Sterianou, Tim P. Comyn, and Andrew J. Bell
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Phase boundary ,Materials science ,Analytical chemistry ,General Physics and Astronomy ,Mineralogy ,Dielectric ,Lead zirconate titanate ,Piezoelectricity ,Ferroelectricity ,chemistry.chemical_compound ,chemistry ,visual_art ,visual_art.visual_art_medium ,Curie temperature ,Ceramic ,Solid solution - Abstract
Ceramics around the morphotropic phase boundary (MPB) in the (1−x)BiSc1−yFeyO3–xPbTiO3 solid solution were fabricated. For y=0.5, ceramics were single phase, and piezoelectric coefficients (d33) and electromechanical coupling coefficients (kp) for MPB compositions were 300 pC/N and 0.49, respectively; a level of piezoelectric activity similar to that of hard, lead zirconate titanate compositions but with TC∼60 °C higher at ∼440 °C. For ceramics with y≥0.7, dielectric measurements in combination with diffraction contrast transmission electron microscopy revealed the existence of two ferroelectric phases for most PbTiO3 contents studied. The presence of two ferroelectric phases was associated with a decrease in piezoelectric activity and although raw materials costs for y=0.7 and 0.8 with respect to y=0 were significantly lower (less Sc2O3) and TC greater (∼500 °C), d33 (∼100 pC/N) and kp (0.18) were too low to be commercially useful for actuator applications.
- Published
- 2009
19. Relaxor ferroelectric-like high effective permittivity in leaky dielectrics/oxide semiconductors induced by electrode effects: A case study of CuO ceramics
- Author
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Derek C. Sinclair, Ming Li, and Antonio Feteira
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Permittivity ,Copper oxide ,chemistry.chemical_compound ,Materials science ,chemistry ,Annealing (metallurgy) ,Electrical resistivity and conductivity ,General Physics and Astronomy ,Relative permittivity ,Dielectric ,Composite material ,Capacitance ,Dielectric spectroscopy - Abstract
The electrical behavior of copper oxide (CuO) ceramics sintered at 920 °C has been characterized by a combination of fixed, radio frequency (rf) capacitance measurements, and impedance spectroscopy (IS). Fixed rf capacitance measurements on ceramics with sputtered Au electrodes revealed a temperature- and frequency-dependent high effective permittivity of ∼104 in the temperature range of 150–320 K. The response is similar to that observed for relaxor-ferroelectrics, however, the magnitude of the effect can be suppressed by thermal annealing of the ceramics with Au electrodes in air at 300 °C or by changing the work function of the electrode material by using In–Ga as opposed to Au. IS data analysis revealed the ceramics to be electrically heterogeneous semiconductors with a room temperature dc resistivity
- Published
- 2009
20. Possible incipient ferroelectricity in Mn-doped Na1/2Bi1/2Cu3Ti4O12
- Author
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Derek C. Sinclair, Matthew C. Ferrarelli, and Anthony R. West
- Subjects
Permittivity ,Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Orders of magnitude (temperature) ,Ferroelectric ceramics ,Inorganic chemistry ,Doping ,Relative permittivity ,chemistry.chemical_element ,Manganese ,Ferroelectricity ,chemistry ,visual_art ,visual_art.visual_art_medium ,Ceramic - Abstract
The grain semiconductivity of Na1/2Bi1/2Cu3Ti4O12 ceramics is suppressed by several orders of magnitude by Mn-doping and Na1/2Bi1/2Cu2.82Mn0.18Ti4O12 ceramics exhibit high room temperature relative permittivity, er, ∼140. er data at 100 kHz fit the Barrett equation over the range ∼10–320 K and the magnitude and temperature dependence of er are consistent with incipient ferroelectricity in this compound.
- Published
- 2009
21. Influence of octahedral tilting on the microwave dielectric properties of A3LaNb3O12 hexagonal perovskites (A=Ba, Sr)
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Neil McN. Alford, Neil C. Hyatt, Kumaravinothan Samara, Derek C. Sinclair, Andrew J. McQueen, Emma E. McCabe, Lisa J. Gillie, Ritesh Rawal, Ian M. Reaney, and Antonio Feteira
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Permittivity ,Crystallography ,Materials science ,Physics and Astronomy (miscellaneous) ,Octahedron ,Rietveld refinement ,Neutron diffraction ,Space group ,Crystal structure ,Dielectric ,Temperature coefficient - Abstract
Rietveld refinement of room temperature (RT) neutron diffraction (ND) data reveals 12R-type hexagonal perovskites Ba3LaNb3O12 (BLN) and Sr3LaNb3O12 (SLN) to adopt space group R3¯ with tilted NbO6 octahedra. The presence of an octahedral tilt transition (Ttilt) at 465 K in BLN from R3¯ to R3¯m is proposed from a combination of high temperature ND data and fixed frequency permittivity measurements. Ttilt is estimated to be much higher at ∼720 K for SLN. The large difference in the RT temperature coefficient of the resonant frequency (τf), −100 ppm/K for BLN compared to −5 ppm/K for SLN, is attributed to the closer proximity of Ttilt to RT for BLN. τf in these 12R-type hexagonal perovskites can therefore be tuned by controlling the tolerance factor and therefore Ttilt in a manner similar to that used for many Ba- and Sr-based 3C-type ABO3 perovskites.
- Published
- 2009
22. Incipient ferroelectricity and microwave dielectric resonance properties of CaCu2.85Mn0.15Ti4O12 ceramics
- Author
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Ming Li, Derek C. Sinclair, Anthony R. West, and Antonio Feteira
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Permittivity ,Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Ferroelectric ceramics ,Dielectric ,Ferroelectricity ,Nuclear magnetic resonance ,Electrical resistivity and conductivity ,visual_art ,visual_art.visual_art_medium ,Ceramic ,Temperature coefficient ,Microwave - Abstract
Mn-doped CaCu3Ti4O12 ceramics with nominal composition CaCu2.85Mn0.15Ti4O12 (CCMTO) have been prepared and their radio- and micro-wave dielectric properties established. At 300 K, dense CCMTO ceramics have appreciable grain resistivity, ∼20MΩcm, and exhibit microwave dielectric resonance with er∼93, Qf∼3950GHz (at 3.95GHz) and temperature coefficient of resonant frequency ∼+657ppm∕K. er decreases smoothly from ∼150 to 90 in the range of 10–300K, obeys the Curie-Weiss law in the range of ∼60–180K, and is consistent with incipient ferroelectricity. The source of the incipient ferroelectricity and potential applications of CCMTO ceramics are discussed.
- Published
- 2007
23. In situ Raman spectroscopy of A-site doped barium titanate
- Author
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Ian M. Reaney, O. P. Thakur, Derek C. Sinclair, U. M. Pasha, Karl R. Whittle, H. Zheng, and Antonio Feteira
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Phase transition ,Materials science ,Physics and Astronomy (miscellaneous) ,Ferroelectric ceramics ,Analytical chemistry ,Mineralogy ,Dielectric ,Ferroelectricity ,Tetragonal crystal system ,chemistry.chemical_compound ,symbols.namesake ,chemistry ,Phase (matter) ,Barium titanate ,symbols ,Raman spectroscopy - Abstract
Raman spectroscopy has been used to study the ferroelectric tetragonal to paraelectric cubic phase transition Tc in undoped BaTiO3 (BT) and (Ba0.92A0.08)TiO3 [where A=Ca (BCT), Sr (BST), and Pb (BPT)]. In BT and BPT, mode characteristic of the tetragonal phase at 303 and 710cm−1 persisted until >50°C above Tc, indicating the presence of local dynamic polar clusters well above the displacive phase transitions, ∼120 and ∼149°C, respectively. However, in BCT and BST, the Raman spectra exhibited only broad second order bands above Tc, suggesting that Ca and Sr, A-site dopants supress local dynamic polar clusters.
- Published
- 2007
24. Comment on the use of calcium as a dopant in X8R BaTiO3-based ceramics
- Author
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Derek C. Sinclair, Andrew G. Mould, O. P. Thakur, Lei Zhang, Gillian M. Keith, Anthony R. West, and Antonio Feteira
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Materials science ,Physics and Astronomy (miscellaneous) ,Dopant ,Condensed matter physics ,Electrical resistivity and conductivity ,visual_art ,Ferroelectric ceramics ,Doping ,visual_art.visual_art_medium ,Mixed oxide ,Curie temperature ,Ceramic ,Conductivity - Abstract
BaTi1−xCaxO3−x ceramics, where 0⩽x⩽0.04, prepared by the mixed oxide route at 1500°C display a strong suppression of the Curie temperature and a significant increase in grain conductivity with increasing x. The ramifications of these results on the applicability of using Ca2+ as a dopant to achieve X8R specification in BaTiO3-based formulations are discussed.
- Published
- 2007
25. Structural and electrical characterization of CeAlO3 ceramics
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Derek C. Sinclair, Michael T. Lanagan, and Antonio Feteira
- Subjects
Permittivity ,Crystallography ,Tetragonal crystal system ,Materials science ,Electron diffraction ,Polarizability ,Analytical chemistry ,General Physics and Astronomy ,Relative permittivity ,Dielectric ,Microstructure ,Grain size - Abstract
The crystal structure and electrical properties of CeAlO3 ceramics prepared by the mixed oxide route have been investigated. X-ray and electron diffraction data show the room temperature structure to be described by the tetragonal I4∕mcm space group [a=5.3253(5)A and c=7.5860(9)A; Z=4, and theoretical density, Dx=6.64g∕cm3]. CeAlO3 ceramics sintered at 1500°C under flowing 5%H2–95%N2 gas for 4h reach ∼94% of Dx with a microstructure of randomly distributed equiaxed grains of average grain size ∼2μm. Conventional transmission electron microscopy reveals needle-shaped ferroelastic domains in some grains. The relative permittivity er of CeAlO3 ceramics is ∼18–20 in the range of ∼10–300K. At room temperature and microwave frequencies, CeAlO3 ceramics exhibit er∼20.7, Qfr∼40117GHz (at 9.5GHz), and τf∼−57ppm∕K. The ion polarizability for Ce3+ is calculated to be 4.46A3. Revised dielectric polarizabilities for rare-earth lanthanides are also presented.
- Published
- 2007
26. High intrinsic permittivity in Na1∕2Bi1∕2Cu3Ti4O12
- Author
-
Timothy B. Adams, Antonio Feteira, Matthew C. Ferrarelli, Derek C. Sinclair, and Anthony R. West
- Subjects
Permittivity ,Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,visual_art ,Inorganic chemistry ,visual_art.visual_art_medium ,Grain boundary ,Ceramic ,Isostructural - Abstract
The electrical properties of Na1∕2Bi1∕2Cu3Ti4O12 (NBCTO) ceramics between ∼8 and 400K are electrically inhomogeneous, consisting of semiconducting grains and insulating grain boundaries, similar to isostructural CaCu3Ti4O12 (CCTO); however, the intrinsic permittivity of NBCTO of ∼250 at 10K is much higher compared to ∼110 for CCTO. Possible explanations for this high intrinsic permittivity are discussed.
- Published
- 2006
27. Influence of Mn doping on the semiconducting properties of CaCu3Ti4O12 ceramics
- Author
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Ming Li, Anthony R. West, Antonio Feteira, and Derek C. Sinclair
- Subjects
Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Orders of magnitude (temperature) ,Doping ,Metallurgy ,Activation energy ,Conductivity ,Dielectric spectroscopy ,Electrical resistivity and conductivity ,visual_art ,visual_art.visual_art_medium ,Grain boundary ,Ceramic - Abstract
Comparison of impedance spectroscopy data for undoped CaCu3Ti4O12 (CCTO) and CaCu2.94Mn0.06Ti4O12 CCMTO ceramics shows Mn doping to suppress the room temperature bulk semiconductivity of ∼0.01Scm−1 for CCTO by six orders of magnitude. The magnitude of and activation energy for bulk conduction in CCMTO are similar to those of the insulating grain boundaries in CCTO ceramics. A model to explain the suppression of the bulk conductivity in CCMTO ceramics is proposed; the grain and grain boundary regions in CCTO ceramics may consist of the same phase but with slightly different compositions.
- Published
- 2006
28. High-temperature (1−x)BiSc1∕2Fe1∕2O3-xPbTiO3 piezoelectric ceramics
- Author
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Tim P. Comyn, Ian M. Reaney, David I. Woodward, Derek C. Sinclair, Andrew J. Bell, Iasmi Sterianou, and David A. Hall
- Subjects
Permittivity ,Phase boundary ,Materials science ,Physics and Astronomy (miscellaneous) ,Mineralogy ,Trigonal crystal system ,Piezoelectricity ,Tetragonal crystal system ,visual_art ,visual_art.visual_art_medium ,Dielectric loss ,Ceramic ,Composite material ,Phase diagram - Abstract
Perovskite-structured ceramics in the (1−x)BiSc1∕2Fe1∕2O3-xPbTiO3 (BSF-PT) system were fabricated for x⩾0.45 in which a morphotropic phase boundary (MPB) occurred between rhombohedral and tetragonal phases at x≈0.50(TC=440°C). Samples close to the MPB gave piezoelectric and electromechanical coupling coefficients of ∼300pC∕N and 0.5, respectively. The low cost of BSF-PT in comparison to (1−x)BiScO3-xPbTiO3 (BS-PT) coupled with its high TC and usable piezoelectric properties suggests future commercial exploitation.
- Published
- 2005
29. Oxygen loss, semiconductivity, and positive temperature coefficient of resistance behavior in undoped cation-stoichiometric BaTiO3 ceramics
- Author
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Derek C. Sinclair, Eloisa Cordoncillo, P. Escribano, Anthony R. West, and Héctor Beltrán
- Subjects
Materials science ,Dopant ,Metallurgy ,General Physics and Astronomy ,Sintering ,chemistry.chemical_element ,Conductivity ,Oxygen ,chemistry ,Electrical resistivity and conductivity ,visual_art ,visual_art.visual_art_medium ,Grain boundary ,Ceramic ,Composite material ,Temperature coefficient - Abstract
Stoichiometric BaTiO3 ceramics fabricated from sol-gel-derived powders and sintered at temperatures ⩽1100°C are highly insulating and electrically homogeneous. At higher sintering temperatures, samples gradually lose oxygen and the conductivity increases as a consequence. The latter phenomena are very sensitive to the furnace atmosphere and are partially reversible during cooling when partial reoxidation can occur. This results in ceramics that are often electrically heterogeneous with insulating surfaces or grain boundaries but semiconducting grain cores. In samples that were heated at 1450°C in N2 and quenched, a positive temperature coefficient of resistance (PTCR) effect was observed, associated with an additional impedance arising from space-charge effects. These results demonstrate that, depending on sample processing, insulating cation-stoichiometric BaTiO3 can instead be semiconducting and under certain circumstances, exhibit a PTCR effect, without the need for donor dopant additives.
- Published
- 2005
30. Origin of the high permittivity in (La0.4Ba0.4Ca0.2)(Mn0.4Ti0.6)O3 ceramics
- Author
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Ming Li, Derek C. Sinclair, and Antonio Feteira
- Subjects
Permittivity ,Crystallography ,Materials science ,Condensed matter physics ,Ferroelectric ceramics ,General Physics and Astronomy ,Relative permittivity ,Activation energy ,Thermal conduction ,Ferroelectricity ,Perovskite (structure) ,Dielectric spectroscopy - Abstract
Single-phase cubic (La0.4Ba0.4Ca0.2)(Mn0.4Ti0.6)O3 (LBCMT) was reported by Jha et al. [J. Solid State Chem. 177, 2881 (2004)] to exhibit an extraordinarily high effective permittivity (eeff∼6980 and 590 at 1 and 100kHz, respectively) at room temperature. According to x-ray-diffraction analysis, the structure of this perovskite can be fully described on the centrosymmetric space-group Pm3¯m, which precludes the occurrence of ferroelectricity. In the present work, impedance spectroscopy has shown that LBCMT exhibits a bulk permittivity, er∼40–45, in accordance with that expected for a cubic, centrosymmetric perovskite. LBCMT is a semiconductor with a bulk resistivity of ∼3kΩcm at 300K and an activation energy for conduction of ∼0.20eV which is consistent with an electron hopping conduction mechanism. Finally, it is demonstrated that the high effective permittivity eeff reported previously is not an intrinsic bulk effect arising from hopping conduction between Mn+3 and Mn+4, but is ultimately associated with...
- Published
- 2005
31. Impedance and modulus spectroscopy of semiconducting BaTiO3showing positive temperature coefficient of resistance
- Author
-
Derek C. Sinclair and Anthony R. West
- Subjects
chemistry.chemical_compound ,Materials science ,Condensed matter physics ,chemistry ,Electrical resistivity and conductivity ,Barium titanate ,General Physics and Astronomy ,Equivalent circuit ,Curie temperature ,Grain boundary ,Electrical impedance ,Temperature coefficient ,Capacitance - Abstract
Polycrystalline barium titanate that has been doped to give a positive temperature coefficient of resistance (PTCR) effect is an inhomogeneous material electrically. Analysis of ac impedance data using the complex impedance plane representation gives the dc resistance of PTCR ceramics. By additional use of the complex electric modulus formalism to analyze the same data, the inhomogeneous nature of the ceramics may be probed. This reveals the presence of two, sometimes three elements in the equivalent circuit. Grain‐boundary and bulk effects may be distinguished from capacitance data: grain‐boundary effects have temperature‐independent capacitances, whereas bulk effects show a capacitance maximum at the Curie point and Curie–Weiss behavior above the Curie point. Both grain‐boundary and bulk effects appear to contribute to the PTCR effect. These results reveal limitations in current theories of the PTCR effect.
- Published
- 1989
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