Publications
343 results found
Whatmore R, 2014, Characterisation of pyroelectric materials, Characterisation of Ferroelectric Bulk Materials and Thin Films, Editors: Cain, Publisher: Springer, Pages: 65-86, ISBN: 9781402093104
Pyroelectrics form a very broad class of materials. Any material which has a crystal structure possessing a polar point symmetry—i.e. one which both lacks a centre of symmetry and has a unique axis of symmetry—will possess an intrinsic, or spontaneous, polarisation and show the pyroelectric effect. The pyroelectric effect is a change in that spontaneous polarisation caused by a change in temperature. It is manifested as the appearance of free charge at the surfaces of the material, or a flow of current in an external circuit connected to it. The effect is a simple one, but it has been used in a range of sensing devices, most notably uncooled pyroelectric infra-red (PIR) sensors, and has thus come to be of some engineering and economic significance, enabling a wide range of sensing systems, ranging from burglar alarms through FTIR spectroscopic instruments to thermal imagers.
Deepak N, Caro MA, Keeney L, et al., 2014, Interesting evidence for template-induced ferroelectric behavior in ultra-thin titanium dioxide films grown on (110) neodymium gallium oxide substrates, Advanced Functional Materials, Vol: 24, Pages: 2844-2851, ISSN: 1616-301X
The first evidence for room-temperature ferroelectric behavior in anatase-phase titanium dioxide (a-TiO2) is reported. Behavior strongly indicative of ferroelectric characteristics is induced in ultra-thin (20 nm to 80 nm) biaxially-strained epitaxial films of a-TiO2 deposited by liquid injection chemical vapor deposition onto (110) neodymium gallium oxide (NGO) substrates. The films exhibit significant orthorhombic strain, as analyzed by X-ray diffraction and high-resolution transmission electron microscopy. The films on NGO show a switchable dielectric spontaneous polarization when probed by piezoresponse force microscopy (PFM), the ability to retain polarization information written into the film using the PFM tip for extended periods (several hours) and at elevated temperatures (up to 100 °C) without significant loss, and the disappearance of the polarization at a temperature between 180 and 200 °C, indicative of a Curie temperature within this range. This combination of effects constitutes strong experimental evidence for ferroelectric behavior, which has not hitherto been reported in a-TiO2 and opens up the possibility for a range of new applications. A model is presented for the effects of large in-plane strains on the crystal structure of anatase which provides a possible explanation for the experimental observations.
Whatmore R, Watton R, 2013, Pyroelectric Materials and Devices, Infrared Detectors and Emitters: Materials and Devices, Editors: Capper, Elliott, Publisher: Springer Science & Business Media, Pages: 99-148, ISBN: 9781461516071
Aktas O, Salje EKH, Crossley S, et al., 2013, Ferroelectric precursor behavior in PbSc<sub>0.5</sub>Ta<sub>0.5</sub>O<sub>3</sub> detected by field-induced resonant piezoelectric spectroscopy, PHYSICAL REVIEW B, Vol: 88, ISSN: 2469-9950
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- Citations: 42
Kesim MT, Zhang J, Trolier-McKinstry S, et al., 2013, Pyroelectric response of lead zirconate titanate thin films on silicon: Effect of thermal stresses, JOURNAL OF APPLIED PHYSICS, Vol: 114, ISSN: 0021-8979
Ferroelectric lead zirconate titanate [Pb(ZrxTi1-xO)3, (PZT x:1-x)] has received considerable interest for applications related to uncooled infrared devices due to its large pyroelectric figures of merit near room temperature, and the fact that such devices are inherently ac coupled, allowing for simplified image post processing. For ferroelectric films made by industry-standard deposition techniques, stresses develop in the PZT layer upon cooling from the processing/growth temperature due to thermal mismatch between the film and the substrate. In this study, we use a non-linear thermodynamic model to investigate the pyroelectric properties of polycrystalline PZT thin films for five different compositions (PZT 40:60, PZT 30:70, PZT 20:80, PZT 10:90, PZT 0:100) on silicon as a function of processing temperature (25–800 °C). It is shown that the in-plane thermal stresses in PZT thin films alter the out-of-plane polarization and the ferroelectric phase transformation temperature, with profound effect on the pyroelectric properties. PZT 30:70 is found to have the largest pyroelectric coefficient (0.042 μC cm−2 °C−1, comparable to bulk values) at a growth temperature of 550 °C; typical to what is currently used for many deposition processes. Our results indicate that it is possible to optimize the pyroelectric response of PZT thin films by adjusting the Ti composition and the processing temperature, thereby, enabling the tailoring of material properties for optimization relative to a specific deposition process.
Keeney L, Maity T, Schmidt M, et al., 2013, Magnetic Field-Induced Ferroelectric Switching in Multiferroic Aurivillius Phase Thin Films at Room Temperature, Journal of the American Ceramic Society, Vol: 96, Pages: 2339-2357, ISSN: 0002-7820
Single-phase multiferroic materials are of considerable interest for future memory and sensing applications. Thin films of Aurivillius phase Bi7Ti3Fe3O21 and Bi6Ti2.8Fe1.52Mn0.68O18 (possessing six and five perovskite units per half-cell, respectively) have been prepared by chemical solution deposition on c-plane sapphire. Superconducting quantum interference device magnetometry reveal Bi7Ti3Fe3O21 to be antiferromagnetic (TN = 190 K) and weakly ferromagnetic below 35 K, however, Bi6Ti2.8Fe1.52Mn0.68O18 gives a distinct room-temperature in-plane ferromagnetic signature (Ms = 0.74 emu/g, μ0Hc =7 mT). Microstructural analysis, coupled with the use of a statistical analysis of the data, allows us to conclude that ferromagnetism does not originate from second phase inclusions, with a confidence level of 99.5%. Piezoresponse force microscopy (PFM) demonstrates room-temperature ferroelectricity in both films, whereas PFM observations on Bi6Ti2.8Fe1.52Mn0.68O18 show Aurivillius grains undergo ferroelectric domain polarization switching induced by an applied magnetic field. Here, we show for the first time that Bi6Ti2.8Fe1.52Mn0.68O18 thin films are both ferroelectric and ferromagnetic and, demonstrate magnetic field-induced switching of ferroelectric polarization in individual Aurivillius phase grains at room temperature.
Deepak N, Zhang PF, Keeney L, et al., 2013, Atomic vapor deposition of bismuth titanate thin films, 21st IEEE ISAF, held Jointly with 11th ECAPD and 4th Conference on PFM and Nanoscale Phenomena in Polar Materials, Publisher: AMER INST PHYSICS, ISSN: 0021-8979
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- Citations: 15
Varghese J, Ghoshal T, Deepak N, et al., 2013, Fabrication of Arrays of Lead Zirconate Titanate (PZT) Nanodots via Block Copolymer Self-Assembly, CHEMISTRY OF MATERIALS, Vol: 25, Pages: 1458-1463, ISSN: 0897-4756
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- Citations: 26
Varghese J, Whatmore RW, Holmes JD, 2013, Ferroelectric nanoparticles, wires and tubes: synthesis, characterisation and applications, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 1, Pages: 2618-2638, ISSN: 2050-7526
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- Citations: 136
Deepak N, Zhang P, Keeney L, et al., 2012, Atomic vapor deposition of bismuth titanate thin films
C-axis oriented ferroelectric bismuth titanate (Bi 4Ti 3O 12) thin films were grown on (001) strontium titanate (SrTiO 3) substrates by atomic vapour deposition technique. Ferroelectric properties of thin films are greatly affected by the presence of various kinds of defects. Detailed x-ray diffraction data (XRD) and transmission electron microscopy (TEM) analysis showed presence of out-of-phase boundaries (OPBs). These OPBs originate at atomic steps on the SrTiO 3 substrate surface. It is found that the OPB density changes appreciably with the amount of titanium injected during growth of the thin films. © 2012 IEEE.
Palizdar M, Comyn TP, Ward MB, et al., 2012, Crystallographic and magnetic identification of secondary phase in orientated Bi<sub>5</sub>Fe<sub>0.5</sub>Co<sub>0.5</sub>Ti<sub>3</sub>O<sub>15</sub> ceramics, JOURNAL OF APPLIED PHYSICS, Vol: 112, ISSN: 0021-8979
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- Citations: 27
Zhang PF, Deepak N, Keeney L, et al., 2012, The structural and piezoresponse properties of <i>c</i>-axis-oriented Aurivillius phase Bi<sub>5</sub>Ti<sub>3</sub>FeO<sub>15</sub> thin films deposited by atomic vapor deposition, APPLIED PHYSICS LETTERS, Vol: 101, ISSN: 0003-6951
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- Citations: 37
Keeney L, Kulkarni S, Deepak N, et al., 2012, Room temperature ferroelectric and magnetic investigations and detailed phase analysis of Aurivillius phase Bi<sub>5</sub>Ti<sub>3</sub>Fe<sub>0.7</sub>Co<sub>0.3</sub>O<sub>15</sub> thin films, JOURNAL OF APPLIED PHYSICS, Vol: 112, ISSN: 0021-8979
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- Citations: 10
Varghese J, O'Regan C, Deepak N, et al., 2012, Surface Roughness Assisted Growth of Vertically Oriented Ferroelectric SbSI Nanorods, CHEMISTRY OF MATERIALS, Vol: 24, Pages: 3279-3284, ISSN: 0897-4756
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- Citations: 23
Keeney L, Groh C, Kulkarni S, et al., 2012, Room temperature electromechanical and magnetic investigations of ferroelectric Aurivillius phase Bi<sub>5</sub>Ti<sub>3</sub>(Fe<sub>x</sub>Mn<sub>1-x</sub>)O<sub>15</sub> (x=1 and 0.7) chemical solution deposited thin films, JOURNAL OF APPLIED PHYSICS, Vol: 112, ISSN: 0021-8979
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- Citations: 52
Varghese J, Barth S, Keeney L, et al., 2012, Nanoscale Ferroelectric and Piezoelectric Properties of Sb<sub>2</sub>S<sub>3</sub> Nanowire Arrays, NANO LETTERS, Vol: 12, Pages: 868-872, ISSN: 1530-6984
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- Citations: 62
Deepak N, Zhang P, Keeney L, et al., 2012, Atomic Vapor Deposition of Bismuth Titanate thin films, 21st IEEE ISAF, held Jointly with 11th ECAPD and 4th Conference on PFM and Nanoscale Phenomena in Polar Materials, Publisher: IEEE, ISSN: 1099-4734
Palizdar M, Comyn TP, Ward MB, et al., 2011, Crystallographic and magnetic identification of secondary phase in orientated Bi<inf>5</inf>Fe<inf>0.5</inf>Co<inf>0.5</inf>Ti<inf>3</inf>O <inf>15</inf> ceramics
Oxide materials which exhibit both ferroelectricity and ferromagnetism are of great interest for sensors and memory applications. Layered bismuth titanates with an Aurivillius structure, (BiFeO3)nBi4Ti 3O12, can possess ferroelectric and ferromagnetic order parameters simultaneously. It has recently been demonstrated that one such example, Bi5Fe0.5Co0.5Ti3O 15, where n = 1 with half the Fe3+ sites substituted by Co3+ ions, exhibits both ferroelectric and ferromagnetic properties at room temperature. Here we report the fabrication of highly-oriented polycrystalline ceramics of this material, prepared via molten salt synthesis and uniaxial pressing of high aspect ratio platelets. Electron backscatter images showed that there is a secondary phase within the ceramic matrix which is rich in cobalt and iron, hence this secondary phase could contribute in the main phase ferromagnetic property. The concentration of the secondary phase obtained from secondary electron microscopy is estimated at less than 2.5 %, below the detection limit of XRD. TEM was used to identify the crystallographic structure of the secondary phase, which was shown to be cobalt ferrite, CoFe2O4. It is inferred from the data that the resultant ferromagnetic response identified using VSM measurements was due to the presence of the minor secondary phase. The Remanent magnetization at room temperature was Mr ≈ 76 memu/g which dropped down to almost zero (M r ≈ 0.8 memu/g) at 460°C, far lower than the anticipated for CoFe2O4. © 2011 IEEE.
Zhang PF, Nagle RE, Deepak N, et al., 2011, The structural and electrical properties of the SrTa<sub>2</sub>O<sub>6</sub>/In<sub>0.53</sub>Ga<sub>0.47</sub>As/InP system, 17th International Conference on Insulating Films on Semiconductors, Publisher: ELSEVIER, Pages: 1054-1057, ISSN: 0167-9317
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- Citations: 7
Correia TM, Kar-Narayan S, Young JS, et al., 2011, PST thin films for electrocaloric coolers, JOURNAL OF PHYSICS D-APPLIED PHYSICS, Vol: 44, ISSN: 0022-3727
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- Citations: 82
Palizdar M, Comyn TP, Ward MB, et al., 2011, CRYSTALLOGRAPHIC AND MAGNETIC IDENTIFICATION OF SECONDARY PHASE IN ORIENTATED Bi<sub>5</sub>Fe<sub>0.5</sub>Co<sub>0.5</sub>Ti<sub>3</sub>O<sub>15</sub> CERAMICS, Joint Conference on IEEE International Symposium on Applications of Ferroelectrics (ISAF/PFM)/ International Symposium on Piezoresponse Force Microscopy and Nanoscale Phenomena in Polar Materials, Publisher: IEEE, ISSN: 1099-4734
Palizdar M, Comyn T, Kulkarni S, et al., 2010, Synthesis of platelets Bi<inf>5</inf>Fe<inf>0.5</inf>Co <inf>0.5</inf>Ti<inf>3</inf>O<inf>15</inf> via the molten salt method
Oxide materials which exhibit both ferroelectricity and ferromagnetism are of great interest. Layered bismuth titanates with a Aurivillius structure, (BiFeO3)n Bi4Ti3O12, can potentially posses ferroelectric and ferromagnetic order paramaters simultaneously. It has recently been demonstrated that one such example, Bi 5Fe0.5Co0.5Ti3O15 where n = 1 with half the Fe3+ sites substituted by Co3+ ions exhibits both ferroelectric and ferromagnetic properties at room temperature. Here we report on the fabrication of well oriented polycrystalline ceramics of this material, via molten salt synthesis and uniaxial pressing of high aspect ratio platelets. Electron backscatter images showed that there is an extra secondary phase within the obtained ceramic which is rich in cobalt and iron. The concentration of the secondary phase obtained from secondary electron microscopy is estimated at less than 2.5 %, below the detection limit of XRD. Further, the sintering temperature was varied and excess addition of bismuth oxide was employed in an attempt to reduce the secondary phase with limited success. The samples have been characterized by X-ray diffraction, polarization-field measurements and SQUID magnetometery as a function of sample orientation. It is inferred from the data that the resultant ferromagnetic response identified using SQUID measurements is due to the presence of the secondary phase. © 2010 IEEE.
Correia TM, Young JS, Whatmore RW, et al., 2010, Investigation of the electrocaloric effect in a PbMg<sub>1/3</sub>Nb<sub>2/3</sub>O<sub>3</sub>-PbTiO<sub>3</sub> relaxor thin film (vol 95, 182904, 2009), APPLIED PHYSICS LETTERS, Vol: 97, ISSN: 0003-6951
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- Citations: 2
Keeney L, Zhang PF, Groh C, et al., 2010, Piezoresponse force microscopy investigations of Aurivillius phase thin films, 4th International Workshop and Satellite Symposium on Piezoresponse Force Microscopy and Nanoscale Phenomena in Polar Materials, Publisher: AMER INST PHYSICS, ISSN: 0021-8979
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- Citations: 29
Palizdar M, Comyn T, Kulkarni S, et al., 2010, Synthesis of platelets Bi<sub>5</sub>Fe<sub>0.5</sub>Co<sub>0.5</sub>Ti<sub>3</sub>O<sub>15</sub> via the molten salt method, IEEE International Symposium on the Applications of Ferroelectrics (ISAF), Publisher: IEEE, ISSN: 1099-4734
Ashley GM, Kirby PB, Butler TP, et al., 2010, Chemically Sensitized Thin-Film Bulk Acoustic Wave Resonators as Humidity Sensors, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, Vol: 157, Pages: J419-J424, ISSN: 0013-4651
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- Citations: 15
Chang HHS, Whatmore RW, Huang Z, 2009, Pyroelectric effect enhancement in laminate composites under short circuit condition, JOURNAL OF APPLIED PHYSICS, Vol: 106, ISSN: 0021-8979
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- Citations: 13
Correia TM, Young JS, Whatmore RW, et al., 2009, Investigation of the electrocaloric effect in a PbMg<sub>2/3</sub>Nb<sub>1/3</sub>O<sub>3</sub>-PbTiO<sub>3</sub> relaxor thin film, APPLIED PHYSICS LETTERS, Vol: 95, ISSN: 0003-6951
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- Citations: 184
Arai S, Wilson SA, Corbett J, et al., 2009, Ultra-precision grinding of PZT ceramics-Surface integrity control and tooling design, INTERNATIONAL JOURNAL OF MACHINE TOOLS & MANUFACTURE, Vol: 49, Pages: 998-1007, ISSN: 0890-6955
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- Citations: 24
Haigh RD, Whatmore RW, 2009, On the processing conditions and interfacial chemistry of composite PZT thick films on platinised silicon substrates, SENSORS AND ACTUATORS A-PHYSICAL, Vol: 151, Pages: 203-212, ISSN: 0924-4247
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- Citations: 3
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