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Title: Synthesis and Characterization of Modified Lead Calcium Titanate Ceramics and Laser Ablated Thin Films
Authors: Singh, Sarabjit
Supervisor: Prakash, Chandra
Raina, K. K.
Keywords: Ferroelectrics;Titanium;Microwave Sintering;Physics and Material Science
Issue Date: 10-Nov-2006
Abstract: Lead titanate (PbTiO.~) [usually referred as PT] ceramics exhibit many attractive properties. These attributes make them attractive for devices in malay electronic applications in the form of bulk. thin fihn. composite and single crystal. Because simple perovskite structure, PT has been widely used as a model system to understand various phenomena related to cubic to tetragonal phase transition, which takes place abom 490°C from high temperature cubic phase (Pm3m) to a tetragonal (P4mm) ferroelectric phase and is accompanied by,' au abrupt anomaly in electric pcmaittix, ity. the spontaneous polarization, specific heat etc. In its tetragonal form, the lattice anisotropy (c/a) is 1.063. On cooling through Curie temperature (T~), large anisotropy of this ceramic material becomes flagile. In addition, it is difficult to pole it due to high coerci\ c force. However, if PT is doped with isovalent or aliovalent dopants, the c/a ratio decreases and then modified PT can be synthesized using standard processes. Among the dopants, the substitntion of alkaline and rare earth metals for lead results in the higher electromechanical anisotropy (kjkp). This large ratio of thickness to lateral electromechanical-coupling coeflScient in PT is useful in high frequency transducer geometries where lateral coupling between elements is not desired. The addition of calcium or samarium (as dopants or modifiers) into PT results in a higher kt/kp ratio as compared to lead zirconate titanate (PZT) ceramics. This property \xidelx makes it possible that PT based materials can be used for high-flequency applications such as Surface Acoustic Wave (SAW) devices and piezoelectric transti~rmers. Moreover, in the calcinm modified lead titanate (PCT) materials, substitution of results in decreasing cubic to tetragonal phase transformation temperature and suitable amount it can be brought down to room temperature. Lowering of Tc results in material (PCT ceralnics) with higher dielectric constant and larger remnant polarization at room telnperature. Because of these remarkable characteristics, wc believe that modified PC'I" ceramics might be a potential candidate in many electrical and electronic applications. It is generally considered that about 24 tool concentration of calcium allows cracking to be avoided while still having good ferroelectric properties suitable many applications. Also 2 tool Mna' ion snbstimtion in PT ceramics improves the densification. Hence various modified compositions of PCT ceramics I\~itb the substitution of Sin, La and Ta) were prepared to investigate the t~rthcr in~provcmcnt various properties of PCT ceramics with fixed amount of Ca (24 tool) and Mn tool) and Mn tool. In the thesis work, Sm, La and Ta modified lead calcium titanate (PCT) ceramics were prepared by conventional ceramic technique and characterized for various structural, dielectric, fereoelectric and piezoelectric properties. Some novel techniques (microwave sintering and mechano-chemical alloying) were aslo adoped to prepare and characterize Sm modified PCT ceramics to study the above-mentioned properties. Dense and crack free Sm modified PCT thin films were also fabricated using laser ablation technique and characterized for structural, electrical and ferroelectric properties.
Description: Ph.D. Thesis, supervised by Dr. K. K. Raina, Professor, School of Physivs & Materials Science, Thapar Institute of Engineering & Technology, Patiala and Dr. Chandra Prakash, Solid State Physics Laboratory, Delhi April 2005
Appears in Collections:Doctoral Theses@SPMS

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