Investigation of Dielectric Relaxation Processes in Ba₂NdFeNb_4-xTa_xO₁₅Ceramics

Abstract

Dielectric response of Ba 2 NdFeNb 4-x Ta x O 15 (x 0.3, 0.6 and 2) solid solutions with Tetragonal Tungsten Bronze structure has been investigated by means of broadband dielectric spectroscopy in the frequency range from 20 Hz to 37 GHz. Pure Ba 2 NdFeNb 4 O 15 compound displays ferroelectric behavior. Substitution of Nb 5C by Ta 5C considerably alters dielectric response of this system. Ferroelectric state was observed only for x 0.3 compound with slightly lowered ferroelectric phase transition temperature. Further increase of x causes formation of relaxor state in these solid solutions and considerably lowers corresponding dielectric permittivity dispersion temperature region.

Relaxor-to-Ferroelectric Crossover and Disruption of Polar Order in “Empty” Tetragonal Tungsten Bronzes

“…The presence of both frequency dependent, relaxor-type and normal, frequency independent peaks has been observed in the permittivity-temperature profile of a number of TTB compositions. ,,− However, the relaxor-like response in these is often subtle or convoluted with the main permittivity peak associated with T C and has not been demonstratively linked to changes in the structural or P – E properties, and so, the origins of such behavior has not been convincingly assigned. The pronounced separation of the features presented here for Ba 4 La 0.67 □ 1.33 Nb 10 O 30 in conjunction with observed structural variations and changes in P – E behavior provides a valuable opportunity to elucidate the origins of such behavior in the context of the recent crystal-chemical model for relaxor versus normal ferroelectric behavior as a function of composition in TTBs .…”

“…19,37,[64][65][66][67][68][69][70][71] However, the relaxor-like response in these is often subtle or convoluted with the main permittivity peak associated with T C and has not been demonstratively linked changes in the structural or P-E properties and so the origins of such behavior has not been convincingly assigned. The pronounced separation of the features presented here for Ba 4 La 0.67 !…”

Local Structure and Order–Disorder Transitions in “Empty” Ferroelectric Tetragonal Tungsten Bronzes

“…The relaxor to ferroelectric crossover has been studied in a number of other TTB systems attributing the origin of the behavior to the average cation size within the A-sites − or the anionic sublattice. , These studies all identify the disruption of long-range structural order, specifically incommensurate tilt modulations ,, or anion disordering as observed in commensurate Ba 4 R 0.67 Nb 10 O 30 “empty” TTBs, as the driver for the onset of relaxor behavior.…”