NMR Evidence for the Coexistence of Order-Disorder and Displacive Components in Barium Titanate

Abstract

A quadrupole coupling induced 47Ti and 49Ti satellite background which transforms into well-defined satellite lines below T(c) in the ferroelectric phase has been observed in the cubic phase of an ultrapure BaTiO3 single crystal. The results demonstrate the coexistence of a displacive and order-disorder component in the phase transition mechanism and tetragonal breaking of the cubic symmetry due to biased Ti motion between off-center sites in the paraelectric phase above T(c).

Picosecond View of Microscopic-Scale Polarization Clusters in ParaelectricBaTiO3

“…The cluster is a dynamic correlated region where unit cells polarize coherently. NMR experiment [7] showed a relaxation time of Ti ion at each off-center site to be about 10 ns at a temperature of 5 C. On the other hand, hyper-Raman experiment [5] showed the relaxation time of the overdamped phonon to be an order of several hundreds of picoseconds in the same temperature region. Thus, an order of nanoseconds might be a measure of the relaxation time of cluster.…”

“…Although experiments such as neutron scattering [10], x-ray scattering [4,11], and optical birefringence [12,13] showed strongly fluctuating polarizations existing in paraelectric phase of BaTiO 3 near T c , however, such clusters have never been directly observed to date. The reason lies in the fact that the relaxation time of a particular cluster, around an order of nanoseconds [5,7], is too short compared to the general measuring time in practice. Traditional diffuse x-ray scattering or neutron scattering cannot be used to observe the dynamic correlation length, since where the spatial correlation has been averaged by the much longer time for measurement.…”

“…As measured by HyperRaman spectroscopy [5,6], a relaxational dynamics was also observed in the paraelectric BaTiO 3 near T c . NMR experiment [7] has recently shown that Ti ion in the paraelectric phase of BaTiO 3 flutters among off-center sites, claiming the coexistence of order-disorder and displacive characters in phase transition of BaTiO 3 as that predicted by simulation [8]. However, it is still not clear for this substance how a stable ferroelectric polarization domain turns up from those paraelectric fluctuating dipole moments, in particular, how the dipoles fluctuations correlate spatially each other and evolve into a ferroelectric domain as T c is approaching.…”

Doping and temperature-dependent optical properties of oxygen-reducedBaTiO3−δ

“…15 In fact, disorder in the form of microscopic clusters of orthorhombic Ti off-center displacements exists already in rhombohedral phase as revealed by Mn 4+ electron paramagnetic resonance (EPR). 16,17 Evidence of both order-disorder and displacive character of the phase transitions in BaTiO 3 has been found by variety of techniques including nuclear magnetic resonance 18 (NMR), extended x-ray-absorption fine structure (EX-AFS), x-ray-absorption near-edge structure 15 (XANES), Raman 19 and IR 20 spectroscopy. It becomes obvious, therefore, that both resonant (optical phonons) and nonresonant (relaxation) modes have to be considered in the problem of electron-lattice interaction in BaTiO 3 .…”

Phase transition and random-field induced domain wall response in quantum ferroelectrics SrTi18O3: review and perspective

“…This problem can be solved by measuring the electric field gradient (EFG) tensor by Ti NMR [39]. Fig.…”