Byeong-Eog Jun

Acoustic anisotropy in uniaxial tungsten bronze ferroelectric single crystals studied by Brillouin light scattering

Acoustic properties were investigated for four tungsten bronze (TB) uniaxial ferroelectric crystals, i.e., (Sr0.61Ba0.39)5Nb10O30 (SBN61), Cu-doped (K0.5Na0.5)1.0(Sr0.75Ba0.25)4.5Nb10O30 (KNSBN:Cu), K5.80Li3.82Nb10.12O30, and K4.74Li3.07Nb10.44O30 of which the spontaneous polarization is directed along the polar c axis. Large acoustic anisotropy between the two elastic constants C11 and C33 have been observed from all samples. C33 exhibits a significant softening on approaching the diffuse phase transition temperature from high-temperature side while C11 does not show any substantial change in the same temperature range. This softening is accompanied by substantial growth of hypersonic damping, appearance and growth of central peak (CP), and slowing down of the relevant dynamics of CP represented by the reducing half width. All these results indicate that the lattice motions along the c axis couple strongly to the one-component order parameter of the polar nanoregions (PNRs) or precursor polar clusters wh...

Characterizations of Sodium Modified Potassium Lithium Niobate Crystal

Na modified potassium lithium niobate Na 0.23 K 2.60 Li 1.82 Nb 5.35 O 15 (NKLN) crystal has the completely filled tetragonal tungsten bronze structure. Its spontaneous polarization was considered to be P 1 = P 2 = 0 and P 3 2 ≠ 0 below the Curie temperature of 480°C. The Debye-like dipolar relaxations were sustained in the Curie temperature range 460°C – 560°C. The dielectric maximum became smeared and shifted to higher temperature side with the frequency increasing. The Jonscher type low frequency dispersion was dominated in the low frequency range. The NKLN crystal was considered to display the dielectric relaxation due to the space charge and the quenched random fields during the ferroelectric phase transition.

Ferroelectric and Dielectric Properties of (1−x)K0.5Na0.5NbO3 –(x/5)Na0.2K2.8Li2Nb5O15 Composite Ceramics

Alkaline niobates ANbO3 (A = K, Li and Na) display multiple phases coexisting, i.e., perovskite (Pe), LiNbO3, completely filled tetragonal tungsten-bronze (cf-TTB) structures. The composite ceramics of K0.5Na0.5NbO3 (KNN) and Na0.2K2.8Li2Nb5O15 (NKLN) were explored as a candidate for the lead-free dielectric and piezoelectric composite ceramics with only the Pe and the cf-TTB structure coexisting. The Pe and the cf-TTB structure showed the ferroelectric distortions along the c-axis with pseudo-tetragonal symmetry. The (1-x)KNN-(x/5)NKLN (x = 0–0.1) composite ceramics displayed the ferroelectric hysteresis at room temperature. We studied the two phases mixing mechanism by comparing the structural and ferroelectric properties.

Dielectric characterizations of alkali niobates Li4(1−x)Na4xKNb5O15 (x = 0.25–0.75) ceramics

Li4(1?x)Na4xKNb5O15 (LNKN, x = 0.25, 0.5, 0.625 and 0.75) ceramics were synthesized by conventional solid-state reaction method and studied as composite ceramics. The study considered that the LNKN ceramics are the mixed phase of perovskite (Pe) based (Na,K)NbO3(NKN), tetragonal tungsten bronze (TTB) based K3Li2Nb5O15 (KLN) and LiNbO3. The effects of mixed phase contribute to the dielectric properties at temperatures around Tmax for the LNKN ceramics. Dielectric maximum occurs at a temperature around Tmax=500??C irrespective of the Li/Na composition. The largest dielectric maximum ? maxwas observed in LNKN(x = 0.625) ceramics. Dielectric maximum ? max seems to be proportional to the volume fraction of Pe based NKN phase. The second dielectric anomaly occurs at lower temperatures TT?O. The variation of TT?O seems to be caused by the change in Na/K content in the NKN phase.