About cookies on this site Our websites require some cookies to function properly (required). In addition, other cookies may be used with your consent to analyze site usage, improve the user experience and for advertising. For more information, please review your options. By visiting our website, you agree to our processing of information as described in IBM’sprivacy statement. To provide a smooth navigation, your cookie preferences will be shared across the IBM web domains listed here.
Publication
Physical Review B
Paper
Quantum ferroelectricity in K1-xNaxTaO3 and KTa1-yNbyO3
Abstract
The effect known as ferroelectricity arises when forces between polarizable ions in a solid produce a spontaneous displacement of these ions which results in a lattice polarization below some characteristic (Curie) temperature. Fluctuations in this polarization may be thermally induced as in the case of classical ferroelectrics, or if the Curie temperature is near O K, the fluctuations can be due to quantum-mechanical zero-point motion. The term "quantum ferroelectric" is applied to those systems where fluctuations in the polarization result from the zero-point motion. Experimental determinations of variations in the dielectric constant, spontaneous polarization, and elastic compliance as a function of temperature and impurity concentration are reported for K1-xNaxTaO3 and KTa1-yNbyO3, and these results show that the physical properties of quantum ferroelectrics differ from those of classical ferroelectrics in the following ways: First, for a quantum ferroelectric, the transition temperature depends on impurity concentration (i.e., on an effective order parameter) as Tc (x-xc)12, as opposed to Tc (x-xc) for the classical case. Second, the inverse dielectric constant varies with temperature as -1 T2 for the quantum-mechanical case, instead of -1T. Finally, the distribution of transition temperatures in a given macroscopic sample with a Gaussian impurity concentration distribution is p(Tc)Tcexp(-Tc4) for the quantum ferroelectric, as opposed to a Gaussian for the classical situation. These results are in agreement with previous theoretical predictions of some of the distinguishing characteristics of quantum ferroelectricity. © 1979 The American Physical Society.