Preparation and dielectric properties of the lead-free BaFe1/2Nb1/2O3 ceramics obtained from mechanically triggered powder

Abstract

Abstract. In the paper the influence of mechanical activation of the powder on the final dielectric properties lead-free Ba(Fe 1/2 Nb 1/2 )O3 (BFN) ceramic was examined. The BFN ceramics were obtained by 3-steps route. Firstly, the substrates were pre-homogenized in a planetary ball mill. Than, the powder was activated in vibratory mill (the shaker type SPEX 8000 Mixer Mill) for different duration between 25 h and 100 h. The influence of the milling time on the BFN powder was monitored by X-ray diffraction. The diffraction data confirmed that the milling process of the starting components is accompanied by partial synthesis of the BFN materials. The longer of the high-energy milling duration the powders results in increasing the amount of amorphous/nanocrystalline content. The mechanically activated materials were sintered in order to obtain the ceramic samples. During this temperature treatment the final crystallisation of the powder appeared what was confirmed by XRD studies. The performed dielectric measurements have revealed the reduction of the dielectric loss of the BFN ceramics compared to materials obtained by classic methods.

Investigations of BaFe0.5Nb0.5O3 nano powders prepared by a low temperature aqueous synthesis and resulting ceramics

“…All samples show rising permittivity and tan δ values with temperature. Additionally the ceramics sintered at 1200 and 1350 °C exhibit a sigmoidal development, which was also found in other investigations of BaFe 0.5 Nb 0.5 O 3[5,11,67,68]. The sample sintered at 1350 °C shows between 25 °C and about 100 °C only a slight increase of the permittivity from 48000 to 64000, which rises to 230000 at 200 °C.…”

Physical properties of lead-free BaFe1/2Nb1/2O3 ceramics obtained from mechanochemically synthesized powders

“…Previously, [13] we have used carbonate as a starting reagent and consequently the calcination step was required to obtained perovskite phase.…”

“…The powder has been uniaxially pressed into disks with the diameter of 8 mm and thickness about 3 mm, with the usage of polyvinyl alcohol as a binder. The compacting (densification) of the BFN ceramic samples was made by a free sintering method under the following conditions: T s = 1350°C, t s = 4 h (according to the previous works [13,15]). …”

“…The methods are related to high production costs and have serious disadvantages (e.g., hightemperature treatment during the technological process results in coarsening and aggregation of the particles or non-stoichiometric composition or nonperovskite structure of the final materials due to the appearance of the volatile element out-diffusion at high temperature). A much less expensive alternative to those techniques is a direct synthesis from respective oxides at room temperature, via mechanochemical reaction [11][12][13]. The room-temperature synthesis lowers fabrication costs, eliminates the undesirable losses of volatile elements and enables the control of chemical and stoichiometry composition.…”

“…Recently, we have prepared and investigated the BFN ceramics obtained from mechanically activated powders [13]. The conventional process of ceramic preparation was modified by the mechanochemical activation of starting reagents (including carbonates).…”