Phase Formation, Structure, and Dielectric Properties of Modified Potassium Sodium Niobate Ceramics
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e Formation, Structure, and Dielectric Properties of Modified Potassium Sodium Niobate Ceramics G. M. Kalevaa, *, E. D. Politovaa, A. V. Mosunovb, and S. Yu. Stefanovichb aSemenov
Federal Research Center for Chemical Physics, Moscow, 119991 Russia bMoscow State University, Moscow, 119991 Russia *e-mail: [email protected]
Received March 12, 2020; revised April 21, 2020; accepted May 14, 2020
Abstract—We have prepared (1 – x)(K0.5Na0.5)NbO3–xCa(Cu1/3Nb2/3)O3 (x = 0–0.1, ∆х = 0.02) ceramics by solid-state reactions and studied their phase formation, structure, and dielectric and ferroelectric properties. The formation of a phase with the perovskite structure and an orthorhombic unit cell has been demonstrated in all of the samples. Ferroelectric phase transitions have been confirmed by dielectric spectroscopy and laser second harmonic generation measurements. The temperatures of the phase transitions from the orthorhombic ferroelectric phase to the tetragonal ferroelectric phase and to the cubic (paraelectric) phase have been shown to decrease with increasing x. We have analyzed the composition dependences of dielectric parameters in the system studied. Keywords: potassium sodium niobate, ceramics, phase formation, perovskite structure, ferroelectric and dielectric properties DOI: 10.1134/S0020168520100076
INTRODUCTION One topical issue in modern materials research in the high technology era is the development and upgrading of new-generation highly efficient piezoelectric materials capable of mechanical-to-electrical energy conversion and vice versa for applications in aerospace engineering; the nuclear, oil extraction, automobile, aerospace, information, and medical industries; metallurgy; and other areas [1–4]. From the middle of the 20th century through the present, a majority of the most widely used piezoelectric ceramics in many industries are oxide materials based on lead zirconate titanate (PZT) [5–8]. Even though it is in PZT ceramics that the largest piezoelectric charge coefficients d33 and d31 (~370 pC/N) and electromechanical coupling coefficients kt and kp (>60%) so far have been achieved, critical environmental problems stimulated a search for novel, lead-free ceramic materials capable of replacing PZT materials. Competitive materials should meet a large number of requirements: high Curie temperature (TC > 650 K), high remanent polarization, good piezoelectric characteristics, and high stability of functional parameters. In connection with this, potassium sodium niobate solid solutions, (K,Na)NbO3, are among the most attractive environmentally friendly oxide materials [9–16]. Their key advantages include rather high Curie temperatures, TC ~ 700 K, considerably exceeding the temperatures corresponding to the application
area of Pb-containing piezoceramics (below ~450 K), and piezoelectric properties meeting all necessary requirements. Among the (K,Na)NbO3 solid solutions, the composition (K0.5Na0.5)NbO3 (KNN) has aroused most interest because it lies in the region of the morphotropic phase boundary betwe
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