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Dielectric Properties
Published in Daniel D. Pollock, PHYSICAL PROPERTIES of MATERIALS for ENGINEERS 2ND EDITION, 2020
Rochelle salt is a hydrated tartrate with the chemical formula NaKC4H4O6 · 4H2O. It has a complex orthorhombic crystal structure when it is polarized. The ferroelectric axis parallel to the a edge is very high, and unlike KDP compounds, its dielectric constant is a function of temperature. Two sharp Tc peaks occur at about − 18° and +23°C at which ∊ is on the order of 103. The dielectric constants for the b and c directions show a small, linear response to temperature. These have values of ∊ of about 10 in the neighborhood of room temperature. In the range of − 18° to +23°C its structure is monoclinic. The structure is orthorhombic above and below this range. At temperatures below −120°C the dielectric constant parallel to the a direction becomes linear and approaches the values of those of the b and c directions.
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Published in Splinter Robert, Illustrated Encyclopedia of Applied and Engineering Physics, 2017
[acoustics, atomic, energy, fluid dynamics, general, mechanics, quantum] Electromechanical process (i.e., strain) in certain materials. The materials that can produce this effect have specific symmetry features, lattice structure related for instance. Additional effects producing the piezoelectric effect include the stress induced in a material by an applied electric field. The piezoelectric effect was discovered in 1880 by Paul- Jacques Curie (1856–1941) and Pierre Curie (1859–1906). Example materials that possess the piezoelectric effect are quarts, ferroelectric ceramics, and certain salts. Rochelle salt (potassium sodium tartrate: KNaC4H4O6·4H2O first known preparation in the late 1600s by Pierre Seignette (1660–1719), an apothecary of La Rochelle, France; used as a laxative); discovered to have pyroelectric properties by Sir David Brewster (1781–1868) in 1824 later to show piezoelectric properties by the Curie brothers. One specific example of the practical use of the piezoelectric effect is in a quartz-based timing mechanism used in clocks, a battery-operated quartz resonator (also seeultrasound) (see Figure P.87).
Ferroelectric studies for soft Gd-modified PZT ceramics
Published in Phase Transitions, 2018
S. C. Panigrahi, Piyush R. Das, R. N. P. Choudhary
The early discovery of ferroelectricity in some compounds, such as (i) Rochelle salt {NaK(C4H4O6)·4H2O}, (ii) the perovskite group such as barium titanate (BaTiO3), (iii) potassium dihydrogen phosphate (KH2PO4) [1], etc., has motivated researchers to study compounds of similar and/or different structural families in the search of new ferroelectric materials for device applications. Now-a-days lead-free piezoelectric ceramics have been actively investigated but at present they are deficient to completely replace lead-base ceramics which shows huge advantages in real application. Some lead-based compounds of perovskite and other structural families have been found very useful for piezoelectric, pyroelectric and other device applications. Lead zirconate titanate {Pb (Zr, Ti) O3} with different Zr/Ti ratios (abbreviated as PZT) is one of the lead-based ceramics which has extensively been studied by many researchers because of its unique features such as non-hygroscopicity, mechanical strength, high-sensitivity and simplicity of preparation with their excellent piezoelectric, pyroelectric, dielectric and electro-optic properties. Such ceramic material possesses distinct characteristics that make the materials suitable for various applications such as FRAM, MEMS, charge storage, transducer, oscillators, pyroelectric devices, actuators and sensors [2–8].
‘Second’ Ehrenfest equation for second order phase transition under hydrostatic pressure
Published in Philosophical Magazine, 2018
According to Bancroft [6] and Samara [8], of Rochelle salt is equal to 11.0 K/kbar. According to Imai [11], αV at 297 K is equal to 14.9 × 10−5 K−1 (The value of αV is found as the sum of the linear thermal expansion coefficients αa, αb, αc along axes a, b, c taken from Figure 3, Ref [11]) and the volume thermal expansion coefficient jump ΔαV is equal to −1.4 × 10−6 K−1 (αV decreases with increasing temperature). As it follows from Equation (11), ΔζV = −15.4 × 10−14 m2/N. This value can be compared with the compressibility of Rochelle salt in the orthorhombic modification near the transition temperature. The elastic compliances of Rochelle salt are presented in Table 1.
Study on structure and phase transition of an eco-friendly ferroelectric composite prepared from cellulose nanoparticles mixed with Rochelle salt
Published in Phase Transitions, 2019
Hoai Thuong Nguyen, Bich Dung Mai
Rochelle salt (RS) is a classical ferroelectric having two Curie points at −18°C and 24°C with the occurrence of ferroelectric phase between them and can be applied for fabrication of crystal oscillators and transducers due to its strong piezoelectric response [12,13]. As for other classical ferroelectrics, the properties of which are almost entirely explored and no longer attract researchers. However, the introduction of Rochelle salt into nanopores of various matrices as Al2O3 [14,15], molecular sieves [16] and wood [17] is interesting owing to the good maintenance of RS ferroelectric phase even up to the decomposition temperature 56.5°C [14] and the improvement of piezoelectric response [17].