In situ doping of BaTiO₃ and visualization of pressure solution in flux‐assisted cold sintering

Abstract

Cold sintering process (CSP) has attracted great interest due to its extremely low processing temperatures, fast processing times, and simplicity to allow for the densification of ceramics and composites. Understanding the detailed mechanisms underlying low temperature densification is crucial to develop advanced materials and facilitate sustainable and cost-effective industrial implementation to come. Here, by taking BaTiO 3 powder and Sr(OH) 2 •8H 2 O transient chemical flux as a model system, chemical transformation at solid/flux interfaces driving the dissolution-precipitation creep mechanism were investigated. We demonstrate that Sr(OH) 2 •8H 2 O acts both as a sintering flux and a solid solution doping additive, resulting in the formation of BaTiO 3-Ba 1-x Sr x TiO 3 with lower Curie temperatures. Using strontium (Sr) as a tracer chemistry, transmission electron microscopy chemical mapping with energydispersive X-ray analysis indicates that there is a precipitation of a Ba 1-x Sr x TiO 3 mainly at grain/grain interfaces, while grain cores remain undoped. In addition, the difference in the interfacial Sr concentration, which is influenced by the applied uniaxial pressure direction, was clearly observed. This successful visualization of compositional distribution after CSP underlines the significant role of the pressure solution creep in densification process. K E Y W O R D S cold sintering, dielectrics, ferroelectrics How to cite this article: Sada T, Fan Z, Ndayishimiye A, et al. In situ doping of BaTiO 3 and visualization of pressure solution in flux-assisted cold sintering.

Highly Reliable BaTiO3‐Polyphenylene Oxide Nanocomposite Dielectrics via Cold Sintering

“…[ 47 ] The adsorbate molecule/adsorbent surface system is more stable for chemical adsorption, as covalent bonding does occur, and less stable for physical adsorption, as it involves weaker forces such as van der Waals interactions. Given the densification by cold sintering, [ 48 ] the stiff and stable chemical adsorption can affect the interface‐coupled dissolution‐precipitation (Figure 1) kinetics, leading to lower relative densities. Indeed, the use of surfactants with chemical bonding sites impacts the kinetics of cold sintering reaction and decreases the permittivity of cold sintered BaTiO 3 (BT) dramatically.…”

“…Current progress in the cold sintering has also enabled the co‐sintering of dense BaTiO 3 dielectrics with polymer, where polytetrafluorethylene (PTFE) was used for the first demonstration, using alkaline flux as a transient chemical phase. [ 25,26 ] Typically, conventional polymer‐based composites with high permittivity ceramic fillers had relatively low permittivity (less than 100) in the effective volume fraction range (mostly < 60 vol%) of ceramics because the pores and voids are incorporated in the range over 60 vol%. [ 27–29 ] To overcome the low permittivity, artificial nanostructures, such as parallel connectivity (vertical aligned fillers), have been proposed, but it is not favorable for the reliability, since it easily forms the weakest path for a breakdown.…”

Translucent γ-AlOOH and γ-Al2O3 glass-ceramics using the cold sintering process

“…Following this route lead to the preparation of pure zirconia from hydroxide precursors Zr(OH) 4 in just a few minutes at 350 °C [8] . Recent work on BaTiO 3 from Ba(OH) 2 , 8H 2 O precursors also showed high densification rate (95 % relative density) without formation of BaCO 3 [9] . This route offers a great potential for the preparation of metal oxides from low temperature decomposing hydroxides.…”

Assessment of the Role of Speciation during Cold Sintering of ZnO Using Chelates

“…21−26 This mechanism involves stress-enhanced dissolution at highly stressed grain-to-grain contacts, then mass transport through a very thin liquid film, and precipitation at low-stress pore surfaces, following chemical potential gradients. 3,27−29 In spite of much evidence supporting this mechanism in CS, 13,30 additional aspects and details within the various types of chemical routes at the interface are still a subject of debate. In the case of ZnO, a material with particular interest in the materials science community, several assumptions were made.…”

“…Cold sintering (CS) is a recently developed processing technique enabling the low-temperature densification of ceramics, using a solvent and moderate pressures. − Dozens of chemistries and crystal structures, − multicationic compounds, − and composites − were successfully cold-sintered to high relative densities (>92%) at temperatures T < 0.2 T m ( T m : melting temperature), very low as conventional thermally driven techniques operate at temperatures T > 0.5 T m . Densification in CS is mainly driven by pressure solution creep, a deformation mechanism mainly encountered in geochemistry and diagenesis. − This mechanism involves stress-enhanced dissolution at highly stressed grain-to-grain contacts, then mass transport through a very thin liquid film, and precipitation at low-stress pore surfaces, following chemical potential gradients. ,− In spite of much evidence supporting this mechanism in CS, , additional aspects and details within the various types of chemical routes at the interface are still a subject of debate. In the case of ZnO, a material with particular interest in the materials science community, several assumptions were made.…”