Giant room-temperature magnetodielectric coupling in spark plasma sintered brownmillerite ceramics

Abstract

The dielectric, magnetic, and magnetodielectric properties of Ca2FeAO5+δ (A = Al, Ga) ceramics were investigated together with their crystal structures. Rietveld refinement of the X-ray diffraction data indicated that the space group of the Ca2FeAlO5+δ ceramic was Ibm2, whereas that of the Ca2FeGaO5+δ ceramic was Pcmn. Dielectric relaxation above room temperature, originating from the Maxwell–Wagner effect and polaronic hole hopping between Fe3+ and Fe4+ ions, was observed in both ceramics. Weak ferrimagnetic behavior was identified from the magnetic-field-dependent magnetization in these ceramics, which was attributed to the non-cancelled spins of the antiferromagnetic-ordered Fe3+ and Fe4+ ions. An intrinsic, giant, room-temperature magnetodielectric coefficient of up to −23.3% was achieved in the Ca2FeAlO5+δ ceramic at 50 MHz, which was attributed to the suppression of charge fluctuations of Fe3+ and Fe4+ ions in the magnetic field.

Polaron Hopping Induced Giant Room‐Temperature Magnetodielectric Effect in Disordered Rutile NiNb2O6

“…[11b] However, the MD response in these materials usually occurs under high applied magnetic fields or at temperatures far below the room temperature. Although materials with spin-dependent polaron hopping characteristic are found to exhibit high MD response under low applied magnetic fields at room temperature, e.g., La 2 NiMnO 6 (−16%, 300 K, 2 T), [10c] Ca 2 FeGaO 5+δ (−31.7%, 300 K, 1.4 T), [26] Ca 2 FeAlO 5+δ (−26%, 300 K, 1.4 T) [26] and LuFe 2 O 4 (−25%, 298K, 0.1 T), such material is rather scare. The discovery of MD response in r-NiNb 2 O 6 expands the family of MD materials based on spin-dependent polaron hopping while its MD coefficient of −62% is, to the best of our knowledge, nearly two-fold higher than these in existing polaronic systems at room temperature.…”

Local Structures of Oxygen-Deficient Perovskite Sr2ScGaO5 Polymorphs Explored by Total Neutron Scattering and EXAFS Spectroscopy

“…Oxygen-deficient perovskite oxides have been extensively investigated in the last decades because of their rich chemistry, structural complexity, and interesting properties and applications, such as ionic conductors, oxygen sensors, and electrocatalysts. − From the basic perovskite framework, various structure types can be derived, which show different oxygen vacancy orderings or structural distortions. The release of one-sixth of all the oxygen atoms along the [110] direction of the cubic perovskite yields the brownmillerite type structure, with the general formula A 2 BB′O 5 .…”

Oxygen deficient perovskites: effect of structure on electrical conductivity, magnetism and electrocatalytic activity.

“…For the Sr2 compound, the decrease in electrical conductivity as a function of temperature occurs due to the increase in collisions between phonons and charge carriers as the temperature increases. 37 In addition, for this material, the conductivity as a function of temperature has the same descending trend in the entire temperature range, 298 K -1073 K.…”

“…36 Metallic conductivity can be obtained due to the formation of a hybrid band as a result of the enhanced overlap between metal 3d and oxygen 2p bands. [36][37][38] A correlation between conductivity and bond angle is also observed when the x-value is varied in La1-xSrxCoO3. [34][35] A change from semiconductivity to metallic conductivity is observed at x = 0.25.…”

“…Little information is known about the Ca-only analogue, with only magnetodielectric properties reported. 37 Here, we perform neutron diffraction, X-ray photoelectron spectroscopy, and charge-transport studies on both Ca2FeGaO6-δ and CaSrFeGaO6-δ, to demonstrate that the manipulation of defect-order can be used as a tool to control the electrical properties of oxygen-deficient perovskites. CaSrFeGaO6-δ are defect-ordered oxygen-deficient perovskites with brownmillerite-type structure.…”