Quantum Limit of Ferroelectric Phase Transitions inKTa1−xNbx

Low-temperature phase transformations in weakly doped quantum paraelectrics: novel features and quantum reentrant dipolar glass state in KTa0.982Nb0.018O3

“…For y , y mc the transition line T c ¼ f ðyÞ is proportional to ðy -y cr Þ 1=2 and for KTN1.8 the low temperature phase appeared to be ferroelectric with a soft-mode driven displacive type cubic -rhombohedral PT at T C ¼ 27 K (Fig. 1, [8,13]). According to Refs.…”

“…Therefore, the detailed study of KTN with the similar Nb concentration as in KLTN used in [1] is a natural step in this way, and we report here a dielectric permittivity and Raman light-scattering investigations for KTa 0.976 Nb 0.018-O 3 single crystals (KTN1. 8).…”

“…Clustering phenomena with the presence of polar microregions well above T C and appearance of ferroelectric macroregions at T C were stressed in first-order Raman [35 -37] and X-ray diffuse scattering [38] studies. Brillouin scattering experiments revealing a central-peak for KTN 0.9 [39] were considered together with the dielectric relaxation [30,31] and polarization response [40], and have been [8]; (b) phase diagram for KTN for y , 0:07 as determined from measurements of the spontaneous and the temperature variation of the dielectric constant [13].…”

Low temperature structural transformations of dilute KTa 1–x Nb x O 3 : x = 0.018, quantum superparaelectric or reentrant glass scenario?

“…Pure KTaO 3 is one of the model quantum paraelrctrics, in the sense that the cubic paraelectric phase is stabilized at low temperatures by zero-point quantum vibrations, and the crystal does not undergo a phase transition (PT) down to the lowest temperatures [4][5][6]. Substitution of Ta 5+ (ionic radius = 0.617 Å) by Nb 5+ (0.599 Å) [7] in KTa 1-x Nb x O 3 (KTN) induces a polar ordering below a concentration-dependent transition temperature T C emerging at the critical concentration x cr = 0.008, at which T C = 0 K [8,3] (quantum mechanical displacive limit QMDL [9][10][11]). Phase transitions in dilute KTN with 0.008 < x < 0.02 realize nearly to the QMDL.…”

On the Relation of the Order-Parameter and Transition Temperature in Ferroelectric Solid Solutions

“…The presented model can very well elucidate the experimientally observed concentration dependence of the phase transition temperature and the order parameter in substitutionally mixed ferroelectric and quantum paraelectric crystals TSC(CI,Br) [7], K(Νa,Νb)O3 [8], (Pb,Sr)TiO3 [9], (Ba,Sr)TiO :3 [10] as well as tle mixed ferroelectric ceramics (Pb,La)ΤiO3 [11]. Τhe numerical calculations are in good agreement with the experimental findings.…”