Quantum paraelectricity coexisting with a ferroelectric metastable state in single crystals of NaNbO₃: a new quantum effect

Abstract

We experimentally show that, in contrast to the data having been collected so far, some single crystals of NaNbO(3) exhibit a dielectric permittivity of several thousand, at low T, and this value is saturated when approaching 0 K on cooling. Other sodium niobate crystals (having larger dielectric losses) present a first-order phase transition to a ferroelectric phase on cooling (at 80-200 K). The width of the thermal hysteresis in these crystals increases when the temperature of the phase transition obtained on heating decreases. The dielectric permittivity at the phase transition obtained on cooling shows a tendency to increase and saturate, when the thermal hysteresis increases. We identify the ground state of the sodium niobate crystal exhibiting the smallest dielectric losses (in the studied set of crystals) as a novel quantum paraelectric state coexisting with a metastable ferroelectric state. In principle, the crystal presenting the state of quantum paraelectricity can be considered as having the largest (among the crystals studied) thermal hysteresis, for which the low boundary is below 0 K.

Relative phase stability and lattice dynamics of NaNbO3from first-principles calculations

“…Thus, this competition is quite sensitive to changes in the lattice constant by external stress or chemical substitution, which allows some anticipation of the solid-solution phase diagrams on the basis of the endpoint compounds [30]. So, how the competition between the Γ 15 , R 25 and M 3 modes of NaNbO 3 and KNbO 3 behaves as a function of volume is a relevant information for the qualitative understanding of the structural behavior of K 1-x Na x NbO 3 solid solutions. To this end, we calculated the phonon frequencies of both materials at different volumes using the frozen phonon approach.…”

Local structure of NaNbO3: A neutron scattering study

“…This makes formation of large FE domains difficult, resulting in nano-twin states. The large barrier for motion also explains the hysteric effect naturally without invoking the idea of quantum paraelectricity 26 . On the other hand, as we mentioned earlier, replacing Na with other elements such as K can improve its ferroelectric and piezoresponse performance.…”

Modeling charge-imbalancedNaNbO3/SrTiO3superlattices: Lattice relaxation and metallicity

“…For NaNbO 3 , the phase is rhombohedral ferroelectric R3c or orthorhombic paraelectric ͑octahedral rotation a − a − a − , i.e., out-of-phase tilts around all axes͒, depending on whether quantum fluctuations completely suppress ferroelectricity or not. 9 In NaNbO 3 / SrTiO 3 superlattices, an increase in the lattice constant and volume was observed when the number of interfaces is increased. 11 In such a superlattice, the thickness ratio of NaNbO 3 to SrTiO 3 layers was suggested to be 3:1.…”

“…In bulk, both perovskites display complex phase transition sequences as a function of temperature, and they are very close to a ferroelectric transition when 0 K is approached. 8,9 The ground state of both perovskites is affected by ionic zero-point fluctuations. In SrTiO 3 , this phase is tetragonal paraelectric ͑space group I4 / mcm with octahedral rotation sequence a 0 a 0 c − in Glazer's notation, 10 i.e., outof-phase tilting around one axis͒.…”