Browsing by Author "Bijalwan, Vijay"
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- ItemDerivation of losses from impedance spectrum for contour modes of ceramic resonator(TAYLOR & FRANCIS LTD, 2-4 PARK SQUARE, MILTON PARK, ABINGDON OR14 4RN, OXON, ENGLAND, 2020-02) Erhart,Jiří; Bijalwan, Vijay; Maca, Karel; Solař, FilipMethod of loss coefficients calculation from mechanical quality factors of transversal vibration modes is presented. Theoretical formulae are derived for the contour mode of thin square plate and width extensional mode of a thin rectangular plate. Mechanical quality factors are expressed as a function of loss coefficients for ceramic with known Poisson's ratio. Measured impedance spectra are compared with calculations and used for the characterization of losses on lead-free BCZT and lead-based PZT piezoelectric ceramics. Full set of loss coefficients active for planar vibration modes is characterized on a single sample. Mechanical quality factor at resonance is the same for the contour extensional mode of a thin square plate and for the width extensional mode of a thin rectangular plate. Loss coefficients reach the biggest values for the piezoelectric losses, followed by the dielectric and elastic losses. Our results show that the BCZT ceramics have losses of the same magnitude as soft PZT ceramic.
- ItemProcessing of 0.55(Ba0.9Ca0.1)TiO3-0.45Ba(Sn0.2Ti0.8)O-3 lead-free ceramics with high piezoelectricity(WILEY, 111 RIVER ST, HOBOKEN 07030-5774, NJ USA, 2020-03) Bijalwan, Vijay; Tofel, Pavel; Spotz, Zdeněk; Částková, Klára; Sobola, Dinara; Erhart, Jiří; Maca, KarelWe report a large piezoelectric constant (d(33)), 720 pC/N and converse piezoelectric constant (d(33)*), 2215 pm/V for 0.55(Ba0.9Ca0.1)TiO3-0.45Ba(Sn0.2Ti0.8)O-3 ceramics; the biggest value achieved for lead-free piezoceramics so far. The ceramic powders were calcined between 1050 degrees C-1350 degrees C and sintered at 1480 degrees C. The best properties were obtained at a calcination temperature (CT) of 1350 degrees C. The fitting combination of processing and microstructural parameters for example, initial powder particle size >2 mu m, ceramics density similar to 95%, and grain size similar to 40 mu m led to a formation of orthorhombic-tetragonal-pseudo-cubic (O-T-PC) mixed phase boundary near room temperature, supported by Raman spectra, pointed to the extremely high piezoelectric activity. These conditions significantly increase piezoelectric constants, together with high relative permittivity (epsilon(r)) >5000 and a low loss tangent (tan delta) of 0.029. In addition, the d(33) value stabilizes in the range of 400-500 pC/N for all samples calcined between 1050 degrees C and 1250 degrees C. The results entail that the (Ba,Ca)(Sn,Ti)O-3 ceramics are strong contenders to be a substitute for lead-based materials for room temperature applications.