Electrorheological Fluids Based on Bismuth Ferrites BiFeO 3 and Bi 2 Fe 4 O 9
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Electrorheological Fluids Based on Bismuth Ferrites BiFeO3 and Bi2Fe4O9 A. V. Egoryshevaa, A. S. Kraevb, O. M. Gajtkoa, A. E. Baranchikova, *, A. V. Agafonovb, and V. K. Ivanova a
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, 119991 Russia b Krestov Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, 153045 Russia *e-mail: [email protected] Received March 23, 2020; revised March 30, 2020; accepted March 31, 2020
Abstract―A comparative analysis has been made for the dielectric and electrorheological properties of suspensions of highly dispersed powders of bismuth ferrites BiFeO3 and Bi2Fe4O9 in polydimethylsiloxane PMS-300. Dielectric characteristics (dielectric constant, dielectric loss tangent) for the suspensions in frequency range 2.5–106 Hz have been determined and non-Debye character of relaxation processes in these systems has been revealed. The measured values of dielectric constant for the disperse bismuth ferrites at zero and infinite frequency (ε0 and ε∞) are 150 and 59 for BiFeO3, 22000 and 14 for Bi2Fe4O9, respectively. Electrorheological properties of bismuth ferrite suspensions in static electric field (up to 5 kV) in tension, compression, and shear modes have been analyzed. It has been found that the values of electrorheological effect for BiFeO3 suspensions in polydimethylsiloxane PMS-300 are small even at high concentrations of disperse phase (60 wt %). On the contrary, the suspensions of highly disperse Bi2Fe4O9 exhibit distinct electrorheological effect. For 80 wt % Bi2Fe4O9 suspension, the tensile yield point reached ~7 kPa in electric field of 5 kV, while compressive stress was 12 kPa. Keywords: bismuth ferrites, multiferroics, rheology, dielectric suspensions, dielectric materials, dielectric properties DOI: 10.1134/S0036023620080045
INTRODUCTION Electrorheological fluids (ERF) are heterogeneous multicomponent systems comprising a fluid with low dielectric constant and a filler [1–3]. The interest in these materials is caused primarily by a their ability of fast and reversible alteration of viscoelastic characteristics (viscosity, yield point, shear modulus, etc.) in external electric fields. These systems are typical smart materials and promising for application in different fields of mechanical engineering and robotics, in particular, in damping devices, vibration suppressors, hydraulic systems, etc. [4]. The functional properties of ERF are determined by the dipole interaction of polarized particles of disperse phase and formation dynamics of spatial structures in external electric field. Highly dispersed oxides of silicon, titanium, aluminum, graphene, semiconducting polymers, etc., were proposed to use as disperse phases in ERF [5–14]. To date, there are no strict criteria to select disperse phase that provide the maximal electrorheological response of material. At the same time, according to empirical criterion [15, 16], disperse phase particles
should have high dielectric constant
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