Dielectric relaxations in Ho2Ti2O7 and Dy2Ti2O7 pyrochlores

Abstract

Dielectric measurements of Ho2Ti2O7 and Dy2Ti2O7 cubic pyrochlore show two distinctly defined relaxations around 90K and 36K. The nature and possible origin of these relaxations have been determined. The observed value of critical exponent of Curie-Weiss and Lacroix-Bń́ equation confirms these relaxations are diffuse and show Debye-like behavior. The order of activation energy of Ho2Ti2O7 and Dy2Ti2O7 shows that both relaxations are distinctly related with structural distortion at oxygen sites. Temperature-dependent lattice volume shows deviation from Debye-Grüneisen behavior below 70 K, further confirms the structural origin of both relaxations. An underlying crystal field anisotropy induced splitting of multipolar order parameter is the primary cause of both diffuse relaxations in these spin ices. It has been found that dielectric relaxations depend strongly on the crystal field, which provides a tool to fine tune the dielectric properties of these systems.

Relaxor–super-paraelectric behaviour and crystal-field–driven spin-phonon coupling in pyrochlore Eu2Ti2O7

“…On the other hand, similar transitions were observed in the isostructural Ho 2 Ti 2 O 7 at 60 K and 23 K [12]. It was inferred that the higher temperature transitions (i.e., at 25 K for Dy 2 Ti 2 O 7 and 60 K for Ho 2 Ti 2 O 7 ) are related to the structural origin [14]. The lower temperature transitions (23 K for Ho 2 Ti 2 O7 and 13 K for Dy 2 Ti 2 O 7 ) are essentially emerged from the nucleation of the electric dipoles driven by the non-collinear spin ordering [11,13].…”

Compositional influence of local and long-range polarity in the frustrated pyrochlore system Bi2−xRExTi2O7(RE = Y3+,Ho3+)

“…In addition to magnetic properties, this material has been investigated as a multiferroic given the potential for the interaction of magnetic (associated with Ho 3 ) and electrical (associated with the SOJT Ti 4+ ) dipoles. Previous work on single crystals 55 and powders 24 of Ho 2 Ti 2 O 7 indicated an observed ferroelectric transition with a small polarization at approximately 23 K. Previous structural work has indicated that the was no observable change from cubic symmetry through the transition, and pose that the nature of the structural distortion through the observed ferroelectric transition is related to local disorder on both oxygen sites, 56 which they supported with the observation of O'– A–O′ and O–A–O bending modes through IR spectroscopy in other pyrochlores. 57,58 It should be noted that this structural study was performed with X-ray radiation, which is not as sensitive to oxygen positions, but the work provides valuable information on the evolution of the lattice parameters upon cooling.…”

Effect of f–d and d–d Interactions on Dielectric and Optical Properties of Pyrochlore Eu2−xFexTi2O7

“…Similar dielectric relaxation was also observed in isostructural pyrochlore compounds Dy 2 Ti 2 O 7 and Ho 2 Ti 2 O 7 which was referred to as a typical ferroelectric relaxor state. [ 10 ] However, the decrease in the effective Eu–Eu, Eu–Ti, and Eu–O bond lengths and change in Ti–O–Ti bond angles with Fe doping may change the size as well as dynamics of polar regions. To see the effect of Fe doping on polarization, the thermal variation of the relative permittivity ( ε′ ) of ETOF5 and ETOF10 was also collected.…”

“…To date, there are only a few reports available on such pyrochlore lattices, viz., Cd 2 Nb 2 O 7 , Cd 2 Re 2 O 7 , Bi 2 Ti 2 O 7 , Dy 2 Ti 2 O 7 , and Ho 2 Ti 2 O 7 which demonstrated the exhibition of the multiferroicity and/or ferroelectricity originating either from the inherent structural distortion or from the noncollinear spin structures in such systems. [ 6–10 ]…”

“…To date, there are only a few reports available on such pyrochlore lattices, viz., Cd 2 Nb 2 O 7 , Cd 2 Re 2 O 7 , Bi 2 Ti 2 O 7 , Dy 2 Ti 2 O 7 , and Ho 2 Ti 2 O 7 which demonstrated the exhibition of the multiferroicity and/or ferroelectricity originating either from the inherent structural distortion or from the noncollinear spin structures in such systems. [6][7][8][9][10] The pyrochlore A 2 B 2 O 7 system possesses a stable and ordered structure that is distinct from fluorite-type structure. The lattice parameters of the pyrochlore A 2 B 2 O 7 are twice that of CaF 2 .…”