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RESEARCH - HIGHLIGHTS OF PAST AND CURRENT ACHIEVEMENTS
1. NANOPOWDERS OF OXIDE FERROELECTRICS – SYNTHESIS
1.1 Novel Synthetic methodology
Ferroelectric oxides such as Barium titanate (BT) and Lead zirconate titanate (PZT) find extensive applications in electronics. Recent trends in miniaturization of electronic components have led to increased interest in nanosized powders. Synthesis of these by conventional methods is beset with inherent disadvantages such as compositional inhomogeneity, low chemical purity and coarse particle nature. In order to overcome these disadvantages, we have developed a novel direct solution-precipitation method whereby these materials could be synthesized at temperatures as low as 90oC resulting in compositionally homogeneous and nano sized powders with an average particle size less than 50 nm. The novelty in the synthetic methodology resulted in the following two patents;
A PROCESS FOR PREPARATION OF BaTIO3, V.Kumar, Indian Patent – 197127- Granted 4.8.2006
A PROCESS FOR PREPARATION OF STRONTIUM TITANATE POWDERS; V. Kumar, K. J. Stanly, K. Jayan, K. Sivanandan, P. K. Girija; Indian Patent- 215393 –Granted 26.2.2008
Apart from the novelty of the synthetic methodology adopted, this study also featured a comprehensive elucidation of the reaction mechanism for the formation of ferroelectrics at lower temperatures, in the following publication
Solution-Precipitation of fine powders of BaTiO3 and SrTiO3, V.Kumar, J. Am. Ceram Soc., 82(10)2580-2584(1999)
Fig. 1 TEM of a typical BaTiO3 nanopowder
1.2. Applications
Piezoceramics fabricated from Lead Zirconate Titanate system, Pb(ZrxTi1-x)O3 (PZT) –based piezoelectric compositions are extensively used for a wide range of Defence applications such as under water transducers for SONAR, actuators etc. Piezoceramics are also widely used in commercial applications such as Flaw detectors, accelerometers, ultrasonic buzzers, delay lines, medical diagnostic equipments etc. Piezoceramic device manufactures are exploring the possibilities of enhancing the device performance. The performance of piezoceramic components are greatly influenced by the characteristics of the piezoelectric powders, especially their chemical purity and particle size. Nano sized powders are in great demand as they can be processed at relatively lower temperatures and can also be engineered to realize high-density microstructures with enhanced electrical and mechanical characteristics. Therefore, we have synthesised the following piezoelectric compositions based on PZT by the above referred novel method. The powders obtained are chemically pure and nanosized. Piezoceramics obtained from such nanopowders exhibit improved electromechanical characteristics as given below in Table 1.
Advantages of Nanopowders
Lower sintering temperature
Fine-grained and dense microstructures
Enhanced dielectric and electromechanical properties
Fig 2. Fine and coarse-grained microstructures of PZT ceramic and a comparison of their electromechanical characteristics
Table 1 Specifications of Piezoelectric Compositions developed
DEVELOPMENT OF PIEZOCERAMIC COMPONENTS
From the above piezoelectric compositions, some of the important Piezoceramic components developed by us are given in Table-2. Typical dimensions and their important electromechanical characteristics are also given in the table. They are in great demand for Defence and commercial applications.
Fig. 3 Piezoceramic Components – PZT Rings, PZT Plate and PZT Discs
Table 2: Specifications of Piezoceramic Components
*(values given in parentheses are for commercially available equivalent grades)
1.1.3 Industry/End User interaction, Technology transfer etc.
These Piezoelectric materials and Piezoceramic components derived from them were developed to meet the requirements of a premier DRDO laboratory for specific Naval applications. Piezoceramic rings developed by us were used to fabricate transducers for underwater SONARS, tested and approved for transducer fabrication. Technology( TRL-7) is ready for transfer.
The novelty in the piezoelectric compositions resulted in their enhanced electromechanical characteristics, especially one order increase in insulation resistance in comparison with values reported in the literature as well as in commercially available compositions, as well as increased aging-resistance. These novel features led to the following Patents;
1. PIEZOELECTRIC COMPOSITION, METHODS AND APPLICATIONS THEREOF,
A. Anil, V. Priyadarsini, M. Sathyanarayanan and V. Kumar
- US Conventional Patent No.10720565 dated 21.07.2010
- Indian Patent - 434051 – Granted- 7.06.2023
2. FERROELECTRIC GLASS- CERAMICS
In glass-ceramics, a ferroelectric phase is crystallized in a glass matrix through a controlled thermal treatment. Ferroelectric glass-ceramics based on Barium titanate, (Ba1-xSrx)TiO3 [BST] and Lead Zirconatetitanate, Pb(Zr1-x,Tix)O3[PZT] are being increasingly used in RF MEMS applications. In glass-ceramics, if the crystallites are sub micrometer-sized, the temperature dependence of the permittivity and dielectric losses can be considerably minimized. The homogenous nucleation of the ferroelectric crystallites in the glass matrix is important from a device design point of view. For understanding this,a kinetic model was developed. A comprehensive treatment of this has been discussed in our following research publication;
Crystallisation studies and properties of (Ba1-xSrx)TiO3 in borosilicate glass, P.V. Divya and V. Kumar, J.Am.Ceram.Soc. 90, 472-476(2007)
Fig.4 SEM images of the 0.90 BST-0.10(B2O3. x SiO2);a) x= 1( uniformly nucleated BST phase in glass matrix) and b) x=3.
Furthermore, such glass-ceramic compositions were used for thick film ink formulations and a prototype thick film actuator and a capacitor were successfully fabricated and demonstrated.
2.1 Glass-ceramics - Piezoelectric applications
Fig. 5. a) PZT Thick film actuator and b) aunimorph cantilever
Fig. 6. Oscillations of the cantilever as a function of (a) bipolar and (b) unipolar applied AC field
Our important contributions in this area has been published in one of the Chapters entitled “FERROELECTRIC GLASS-CERAMICS” authored by me in the book ADVANCED MATERIALS published by WILEY, May 2014
3. FERROELECTRIC THIN-FILMS
Piezoelectric thin films based on Lead zirconatetitanate (PZT) are extensively used in Micro Electromechanical Systems[MEMS]. One of the important contributions of our research was the fabrication of {100}, {110}, and {111}-preferentially oriented thin films of BaTiO3, PZT, and PLZTthrough appropriate innovations in the sol-gel chemistry of the precursor solutions used for spin-coating thin films. This simple strategy obviated the epitaxial fabrication of preferentially-oriented thin films.
3.1 Applications
3.1.1 Piezoelectric applications
In the case of piezoelectric thin films of PZT, their effective transverse piezoelectric coefficient, e31 is the most important characteristic to be considered forMEMS applications. This measurement, using the most-precise method using Laser interferometer, was carried out at the laboratory of his Japanese collaborator, Prof. I.Kanno, Department of Mechanical Engineering, Kobe University, Kobe, Japan. An important contribution of our research was the establishment of a correlation between thin film texture (preferential orientation) and their transverse piezoelectric coefficient, e31. The in-depth studies clearly provided insights into the switching of ferroelectric polarization which is explained in the following publication.
Sol-gel deposition and Piezoelectric properties of {110}-oriented PZT thin films, D. Ambika, Viswanathan Kumar, Hideyuki Imai and IsakuKanno, Appl. Phys. Lett. 96, 031909(2010)
3.1.2 Phase-shifter applications
Ferroelectric thin films based on Lead titanate (PbTiO3), Barium titanate (BaTiO3) and other related systems are important in the context of applications in phase-shifters for space communications. Their choice for these applications result from the tunability of their capacitance as a function of an applied DC bias voltage(Fig.7).
Ferroelectric thin films based on Lead titanate were successfully developed for Indian Space Research Organisation (ISRO) for their use in Phase-shifters. Thin-films developed by uswere tested and found to give excellent characteristics by Vikram Sarabhai Space Centre[VSSC], Trivandrum [ISRO] and were approved for phase shifter applications.
Unique features
Very high dielectric tunability( 77 %) was realized in (Pb, Sr)TiO3 thin films – Fig.7
Very high dielectric breakdown ( E> 300 kV./cm.) was achieved in (Pb, Sr)TiO3 thin films-Fig.7
Fig. 7, Dielectric tunability of (Pb1-xSrx)TiO3 thin films at 1.0 MHz.
3.2 NLO applications of ferroelectric thin films
Our studies have opened a new pathway for the use of thin films of La3+-doped PZT [PLZT], for NLO applications. Our studies, in collaboration with Prof. Reji Philip, RRI, Bangalore, have shown that PLZT thin films have the potential to be used in the fabrication of miniature photonic devices for optical power limiting, modulation and switching,
Our study has established, for the first time, a correlation between defect chemistry and nonlinear optical absorption in PLZT thin films. This has opened a new pathway for tuning nonlinear absorption in lead titanate -based thin films.
We could clearly provide insights into role of defects in PLZT on its NLO absorption characteristics in the following publication.
Tunability of third order nonlinear absorption in PLZT thin films, D.Ambika, Viswanathan Kumar, C.S. Suchand Sandeep and R.Philip, Appl. Phys, Lett., 98, 011903 2011
4. Other significant achievements
A significant aspect of our research is structure-property correlations in ferroelectric and related materials. Some of our important contributions are listed below;
1. Correlation of the ferroelectric-paraelectric transition temperature, Curie point, Tc with nature of chemical bond in his following publication;
Preparation and dielectric characteristics of nanocrystallineBa(MxTi1-x)O3 ; V.Kumar, I. Packiaselvam, K. Jithesh and P.V. Divya, J. Phys.D: Appl. Phys.40, 2936(2007)
2. Structure-Property correlation in Manganese-doped Pb(Zr,Ti)O3 in his following publication, as part of the Doctoral work of K.P. Rema.
Structure-property relation in Mn3+- doped PZT, K.P. Rema and V. Kumar, J.Am.Ceram.Soc. 91,164-168(2008)
3. On using glass-ceramics as functional materials for thick film inks and using such formulations, for the first time, for fabricating thick film prototype actuators and capacitors in the following publications as a part of the Doctoral work separately of P.V. Divya and K.P. Rema;
a) Fabrication and Tunable Dielectric Properties of (Ba0.70Sr0.30)TiO3- Glass Based Thick Film Capacitors, P.V. Divya, D. Ambika, Dhanya Krishnan, K. Sivanandan and V.Kumar, Int. J. Appl. Ceram. Technol..6,231-235(2009)
b) Fabrication and Transverse Piezoelectric Characteristics of PZT Thick-film Actuators on Alumina substrates,” K. Sivanandan, Asha T. Achuthan , V. Kumar*, IsakuKanno, Sens. Actuators A 148, 134-137(2008)
c) Synthesis and piezoelectric properties of PZT-based glass ceramics, K.P. Rema and V. Kumar, J.Mat.Sci.: Mat. Elec.20,380-385(2009)
4. Comprehensive elucidation of the mechanism responsible for Relaxor to Ferroelectric transition in the relaxorPLZT[8/65/35] in the following publication, as a part of the Doctoral work of A.S. Divya;
A Novel mechanism for Relaxor to ferroelectric transition in PLZT[8/65/35], A.S. Divya and V.Kumar, J.Am.Ceram.Soc,92(9)2029-32(2009)
5.Comprehensive elucidation of the mechanism responsible for Ferroelectric to Relaxor transition in the Ferroelectric PLZT[7/60/40] in the following publication, as a part of the Doctoral work of A.S. Divya;
Influence of Strontium Substitution on Ferroelectric to Relaxor Transition in PLZT (7/60/40), V.Priyadarsini, P.V. Salija, A.S. Divya ,ViswanathanKumar, J. Am. Ceram. Soc., 93 [11] 3584–3586 (2010)
6. Unravelling the influence of defects in ferroelectric BaTiO3 and PZT on their dielectric, ferroelectric and piezoelectric characteristics, in the following research publications, as a part of the Doctoral work of K. Vani and A.Anil
a) Role of Defect Structures in Stabilization of Ferroelectric Phase in Tin-Substituted Lead ZirconateTitanate, A.Anil, K.Vani and V.Kumar, J.Amer.Ceram.Soc. 101,3377-3382(2018)
b) Influence of defect mobility on electrostrain in (Ba0.80Sr0.20)TiO3, K.Vani and V.Kumar, AIP Advances 2,042177(2012)
c) Evolution of Dielectric and Ferroelectric Relaxor States in Al3+-doped BaTiO3 , K.Vani and V.Kumar, AIP Advances 5,027135(2015)
d) Influence of defect structure on Ferroelectric aging in donor-acceptor hybrid doped PZT, A.Anil ,K. Vani and Viswanathan Kumar, Appl. Phys.A, 122,581(2016)
7. Providing clear insights into the local structural rearrangements in the complex perovskite, (Ba1-xPbx)(In0.50Nb0.50)O3, in the following research publication, as a part of the Doctoral work of A.Anil
Evolution of local structural rearrangements in the complex perovskite (Ba1-xPbx)(In0.50Nb0.50)O3, A.Anil and Viswanathan Kumar, J.Amer.Ceram.Soc. 99, 3980-3984(2016)
Ourresearch in semiconducting ZnO has also provided insights into their defect chemistry enabling to unravel their crucial role in some unique characteristics. They are as given below;
8. On the mechanism of NLO absorption in Mg.-doped ZnO thin films in the following publication;
Sol-gel synthesis and non-linear optical transmission in Zn1-xMgxO thin films, C.S.SuchandSandeep, Reji Philip, R. Satheeshkumar and V. Kumar, Appl. Phys. Lett. 89, 063102( 2006)
9. Comprehensive elucidation of mechanism responsible for orange emission in ZnO in the following publication as a part of the Doctoral work of T.AntoJohny;
Influence of Lithium doping on orange emission in Mn.-doped ZnO, T.AntoJohny, and V.Kumar, J.Mat.Sci.: Mat. Elec.,25,1456(2014)
10. Correlation of the defect chemistry with ferromagnetic ordering inZnO-based systems, in the following publications as a part of the Doctoral work of M.K. Satheesan
a) Influence of lithium doping on the correlated ferromagnetic ordering and red shift of band gap in weakly Mn.-doped ZnO nanoparticles, M.K. Satheesan and Viswanathan Kumar, J.Mater.Sci:Mater.Electron. 27,6522(2016)
b) Influence of defects on the ferromagnetic ordering of Niobium-doped ZnO nanoparticles, M.K. Satheesan and Viswanathan Kumar, J.Mater.Sci:Mater.Electron. 28 4719(2017)
c) Acceptor-defect mediated Room Temperature Ferromagnetism in (Mn2+, Nb5+) co-doped ZnO Nanoparticles, M.K. Satheesan and Viswanathan Kumar, Ceram.Intl. 43, 8098(2017)
d) Room Temperature Ferromagnetism and red shift of band gap in (Mn2+, Mg2+) co- doped ZnO Nanoparticles, M K Satheesan, Viswanathan Kumar, J. Mater. Sci: Mater. Electron. 27, 17601(2017)
11. Correlation of the defect chemistry with enhanced visible light photocatalyticdegration of organics in BaTiO3-based systems in the following publication as a part of the Doctoral work of N.Manoj;
a) Manganese doped BaTiO3 nanotube arrays for enhanced visible-light photocatalytic applications, N.Manoj and V.Kumar, Mat.Chem.Phys,213,400-405(2018)
12. On their use as desulpharisation catalysts with enhanced performance
Realising the importance of desulpharisation of petroleum products, to minimize environmental pollution from automobile and industrial exhausts, an industry-led project, funded by DST, was successfully implemented. A semi-pilot process for preparation of NanoZnO, with tailored defect-chemistry, was established. The desulpharisation catalyst developed by the industrial partner,M/S SUD-CHEMIE India Pvt.Ltd., Cochin exhibited excellent catalytic performance, as shown in Table - 3
Some of the innovative aspects in the materials design, especially the particle size control and defect-chemistry exploitation, have resulted in the following Patent.
NANO-ZINC OXIDE, PROCESS OF PREPARATION AND APPLICATIONS THEREOF;
N.Manoj, K.V. Baiju and V.Kumar, Indian Patent - 325691 - Granted 25.11.2019
Fig.8. Nano ZnO and pilot production facility for Nano ZnO
Table 3 Comparitive evaluation of NanoZnO with commercial grade ZnO
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