Structural study of a poled ceramic at low temperature

Neutron diffraction study of electrostrictive coefficients of prototype cubic phase of relaxor ferroelectric PbMg1/3 Nb2/3 O3

“…13 The results of both ZFC and FC experiments are in good agreement with similar experiments performed by other research groups. For ZFC, the crystal lattice of PMN is cubic in the whole studied temperature interval, 7,10 whereas for FC using E ϭ 5 kV/cm the crystal structure is rhombohedral at temperatures below 220 K. 12,14 The transformation of the crystal structure from cubic to rhombohedral at Tр220 K was evidenced, for example, by splitting in the (hhh) reflection into (hhh) and (hhh) under applied field. In both cases, unit cell parameters, a c ͑for cubic͒, and a rh and ␣ rh ͑for rhombohedral͒, were determined using the structural refinement procedure based on the Le Bail adaptation 15 of the Rietveld method.…”

“…High-resolution data were required in order to detect the phase transformation with a very small lattice distortion in the rhombohedral ferroelectric phase of PMN from the prototype cubic phase, (90°Ϫ␣ rh )р0.1°. 14 In order to be able to apply the electric field in the FC experiment, the samples were prepared in the form of a multilayer sandwich, where 15 ceramic disks, each 2 mm thick with 10 mm diameter, were glued together using a conductive epoxy. The experiment was first conducted in the ZFC regime where the diffraction patterns of PMN were recorded at several temperatures from 1050 to 100 K. Afterwards, the dc field E ϭ 5 kV/cm was applied to the same sample at 300 K, then the sample was cooled down ͑FC regime͒, and the diffraction patterns were recorded at several temperatures below T f ϭ220 K, where the field induced phase transition was expected in PMN for the electric field larger than the threshold field, E th ϭ1.7 kV/cm.…”

A crystallographic analysis of the macrodomain structure in Pb(Mg1/3Nb2/3)O3

“…Our calculations have been carried out by using the unit cell parameters of PMN [20,21] measured on ceramic and crystal samples within the phase transition region (a,.h = 4.0400 A, w = 0.07° and ~ = 4.0441 A). A diagram connecting the possible domain types and the _.--.,hapes of the m3m '=t 3m phase boundaries shows a lack of unstrained planes for such a ,,hase matching and a sufficiently vast region related to the conic surfaces ( figure 3 ).…”

“…A comparison of the diagram for the m3m '=t 3m phase transition in PMN crystals (figure 3) with an analogous known diagram for the first-order ferroelectric phase transition in PbZr0 3 crystals [17] allows us to ascertain that the presence of three vast regions belonging to the conic surfaces and the existence of the unusual curve corresponding to the zero-net-strain planes are characteristic of PbZr0 3 crystals. A certain shift of the curves in the diagram by consideration of PMN crystals may be associated with a change in the structural parameters [17,[20][21][22] and with the unit cell spontaneous strains,~;= IJa -I and ~' = IJ, of these crystals at the phase transitions <~:li;' = -0.832 for PMN and~~~~·= 0.523 for PbZr03), which have significant influence on the elements Du of equation (3) and on the invariants of equations (5). 4.…”

Dielectric studies of the electricfield-induced phase transition in ti-doped pb(m91/3nb2/3)o3 ceramics

“…The transition is revealed on the E' = f ( T ) and tgS = f ( T ) curves by an extra-peak at a temperature lower than T,,, and on the X-ray patterns by the appearance of a rhombohedra1 phase. 22 The present work deals with the study of the influence of an external electric field on the polarization of 3.75% Ti-doped PMN ceramics in different runs of thermal evolution in order to better understand the transformation from a polar nanodomain to a polar macrodomain state. The results will be compared with those obtained recently on pure PMN ceramics.23…”