Ultrafast synthesis and densification of ZrO₂ doped KNN ceramics by reactive flash sintering

Abstract

Fabrication of dense KNN‐based lead‐free piezoelectric ceramics at low temperatures in short time through a cost‐effective way remains a challenge. Herein, this challenge could be addressed by using reactive flash sintering. It is demonstrated that the phase transformation of KNbO3‐NaNbO3 into (K,Na)NbO3 and densification occur simultaneously during the flash event. Most importantly, ZrO2 doping can greatly decrease the onset flash temperature, which is ascribed to the increased conductivity of sample. In addition, the current limit has a significant effect on the phase transformation and densification. The flash‐sintered KNN ceramics exhibit the good ferroelectric and piezoelectric properties. Furthermore, the ZrO2 doped and undoped KNN ceramics show a comparable coercive field Ec, which may be related to the residual point defects after the flash. Besides the Joule heating, the avalanche generation of point defects is suggested to be responsible for the ultrafast solid‐state reaction and densification rates.

A versatile defect engineering strategy for room-temperature flash sintering

“…3(b)). Here, after the defect-enriched samples were flash sintered, the defect concentration in the ZnO powders decreased, which was in stark contrast to the abundant defect generation in the previous FS experiments [20][21][22][23]. Moreover, the binding energy of Zn 2+ in the FS-A1 sample before FS occurred was 1020.8 eV.…”

“…Since the thermal runaway effect cannot sufficiently explain the rapid manifestation of FS for just a few seconds, one of the proposed mechanisms for this phenomenon is the electric field-induced formation of Frenkel pairs within the ceramic grains [19]. Su et al [20] reported that a large number of defects were generated in a ZrO 2 -doped K 1-x Na x NbO 3 (KNN) ceramic during FS, with abundant defects remaining in the samples after treatment. The field-induced point defects during FS were discovered to play an important role in the high densification rate, lattice expansion, and microstructural gradients of the ceramics [21][22][23][24].…”

Structural, Vibrational, and Magnetic Characterization of Orthoferrite LaFeO3 Ceramic Prepared by Reaction Flash Sintering

“…Furthermore, Gil-González et al demonstrated the feasibility of employing FS to produce dense and single-phase complex oxides in a single step from their precursors [ 28 ]. This new methodology, which has been denominated Reactive Flash Sintering (RFS), has been recently employed in the preparation of an extensive range of materials, such as ferrites [ 29 , 30 ], ferroelectric materials [ 31 , 32 ], ceramic composites [ 33 , 34 ], high-entropy oxides [ 35 , 36 , 37 ] and solid electrolytes [ 38 , 39 ]. FS and RFS techniques have been also employed for the preparation of LaFeO 3 -based compounds.…”

Flash Sintering Research Perspective: A Bibliometric Analysis

“…This is probably due to the advantages of reduced temperatures and times offered by the technique. A significant number of works have been dedicated to the preparation of high-entropy oxides [111][112][113][114][115], followed by ceramics such as the multiferroic BiFeO 3 and related materials [27,80,116], solid electrolytes [117][118][119], or the lead-free piezoelectric potassium sodium niobate [120,121]. Analogously to Zirconia or ZnO in FS, the underlying mechanisms in RFS have been studied by high-resolution in situ measurements in the reaction of MgO and Al 2 O 3 to form the spinel MgAl 2 O 4 [122,123] .…”