Dynamical properties of the normal phase of betaine calcium chloride dihydrate. I. Experimental results

Abstract

Coherent inelastic neutron scattering results obtained at different temperatures in the normal phase of betaine calcium chloride dihydrate (BCCD) are reported here. The experimental characterization of the mechanism which induces the transition from the parent phase to the incommensurate phase of BCCD is described. We show that the three lower-energy phonon branches of symmetry are temperature sensitive; the lowest of the three displays a conspicuous softening at a wavevector at . The present neutron scattering results are in good agreement with previous Raman and IR measurements.

Flexocoupling-induced soft acoustic modes and the spatially modulated phases in ferroelectrics

“…For example, from the experimental data shown in Fig.3(b) it can be seen that the bend on the lowest acoustic A-mode is absent at 300 K in organic ferroelectric (CH ) NCH COO·CaCl ·2H O. A noticeable minimum appears even at 205 K, and the softening of the A-mode continues at 171 K. The true incommensurate phase occurs at 164 K and coexists with commensurate FE phase from T C = 125 K up to 43 K according to the "devil staircase" scenario [16].…”

“…, for a fixed value of the flexo-coefficient f. A typical scenario is shown in Fig.3(a). The dependence ( ) [8, 13,16,47], and are explained by the interaction of several optical and acoustic modes in proper ferroelectrics [45], as well as by electron-density multiphonon interactions in incipient ferroelectrics [6]. For example, from the experimental data shown in Fig.3(b) it can be seen that the bend on the lowest acoustic A-mode is absent at 300 K in organic ferroelectric (CH ) NCH COO·CaCl ·2H O.…”

“…Basic experimental methods, which contain information about the soft modes and spatial modulation of the order parameter in ferroics (such as antiferroelectrics, proper and incipient ferroelectrics) are dielectric measurements [11], inelastic neutron scattering [5,12,13,14,15,16,17], X-ray [18,19,20,21], Raman [22] and Brillouin [8, 18,21,23,24,25] scatterings and ultrasonic pulse-echo method [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] allowing hypersound spectroscopic measurements.…”

Nanoferroics: State-of-art, gradient-driven couplings and advanced applications (Author’s review)

“…It can be seen from the figure that the magnetoelectric coupling can increase in hundreds and thousands times with decreasing radius. (а) Dependence of the main components of the biquadratic magnetoelectric coupling tensor(12,21,22) on the radius of multiferroic nanoparticle BiFeO 3 . Adapted from Refs [5,10]…”

“…The dependence of an acoustic mode frequency on its wave vector (in the reciprocal lattice constant units π/a). Symbols are experimental data from[ 21 ], measured in the organic ferroelectric…”