Crystalline Mesoporous Complex Oxides: Porosity‐Controlled Electromagnetic Response

Abstract

A colloidal-amphiphile-templated growth is developed to synthesize mesoporous complex oxides with highly crystalline frameworks. Organosilane-containing colloidal templates can convert into thermally stable silica that prevents the overgrowth of crystalline grains and the collapse of the mesoporosity. Using ilmenite CoTiO 3 as an example, the high crystallinity and the extraordinary thermal stability of its mesoporosity are demonstrated at 800 °C for 48 h under air. This synthetic approach is general and applicable to a series of complex oxides that are not reported with mesoporosity and high crystallinity, such as NiTiO . Those novel materials make it possible to build up correlations between mesoscale porosity and surfacesensitive physicochemical properties, e.g., electromagnetic response. For mesoporous CoTiO 3 , there is a 3 K increase of its antiferromagnetic ordering temperature, compared with that of nonporous one. This finding provides a general guideline to design mesoporous complex oxides that allow exploring their unique properties different from bulk materials.complex oxides, in general, has associated kinetic barriers from the slow diffusion in solids. [15] When there are two metal cations involved in crystallization of complex oxides like ABO 3 , their nonuniform distribution can result in spontaneous phase separation to form simple oxides. [16] A delicate balance of their sol-gel rates and the precautious control of thermal annealing procedure is needed. On the other hand, ordering competition between the crystallization of oxides and the mesoscale porosity brings profound difficulties to synthesize complex oxides (e.g., perovskites and ilmenites) with mesoporous structures. Crystallization usually leads to the formation of large crystalline grains that will create strong interfacial energies between crystalline walls and pores (e.g., air or templates). For any templated growth of mesoporous oxides using hydrocarbon-based surfactants or block copolymers (BCPs) as soft templates, [17][18][19] mesoscale nanostructures collapse prior to the crystallization of oxides, [20][21][22] because these soft templates are not mechanically strong and thermally stable under elevated temperatures (i.e., >500 °C).Nanostructures show a profound impact on the magnetic properties of materials as well and a few theoretical models have been proposed to understand magnetic behavior of nanoscale particles. [23][24][25][26][27][28][29][30] The magnetic ordering temperature (Curie temperature or Néel temperature) in magnetic materials

Templated synthesis of crystalline mesoporous CeO2 with organosilane-containing polymers: balancing porosity, crystallinity and catalytic activity

“…Homogeneous gels were observed with a water concentration in the range of 10 vol% to 20 vol%. In additional, the use of PEO 114b-PTMSPMA 224 is of critical importance to preserve the pores of mCeO 2 at high temperature under air [44,50]. Other soft templates like poly(ethylene oxide)-block-polystyrene do not provide similar thermal stability under air [68][69][70].…”

“…On the other hand, our group has developed the use of hybrid polymer templates to overcome the poor thermal stability of organic polymers. The method is simply based on the design of organosilanecontaining block copolymers (BCPs), poly(ethylene oxide)block-poly [3-(trimethoxysilyl)propyl methacrylate] (PEO-b-PTMSPMA) [44][45][46][47][48][49][50]. The PTMSPMA block consists of trimethoxysilyl moieties that can hydrolyze to form polysilsesquioxane and further thermally convert to inorganic silica-like structures [51,52].…”

“…We have demonstrated the use of hybrid polymer templates to grow a few crystalline mesoporous oxides, e.g. TiO 2 [45,50] and titanates [44]. While the interaction of Ti 4+ ions and PEO has been well-understood, the synthetic strategy has been largely limited to Ti-containing crystalline oxides.…”

Metal–Organic‐Framework‐Derived Nanostructures as Multifaceted Electrodes in Metal–Sulfur Batteries

“…Particularly, transition metallic compounds, including transition metallic oxides, sulfides, nitrides, phosphides, etc., are promising materials owing to their fascinating physicochemical performances relying on varying metal cations and inorganic anions. [ 178–187 ] Most transition metallic compounds possess conductivity and polar surfaces applicable for catalytic reaction with sulfur species, therefore, occupying the most significant part in catalytic hosts for MSBs.…”

Structural Engineering in the Self-Assembly of Amphiphilic Block Copolymers with Reactive Additives: Micelles, Vesicles, and Beyond

“…Amphiphilic BCPs containing a reactive block such as poly­[3-(trimethoxysilyl)­propyl methacrylate] (PTMSPMA) have very promising applications to design hybrid polymer nanostructures. − Upon assembly, the hydrolysis of trimethoxysilyl moieties can lead to the formation of silica-like polysilsesquioxane structures with Si–O–Si bonds. Our group has demonstrated the use of amphiphilic BCPs, PEO- b -PTMSPMA, to synthesize crystalline mesoporous metal oxides. − These BCPs as soft templates allow the crystallization of complex oxides up to 1000 °C because of the remarkable stability of these hybrid polymers after the conversion to inorganic silica. However, given their reactivity with moisture, the control over the nanostructures of PTMSPMA-containing BCPs is more difficult to handle compared to conventional BCPs, including the size control of those polymer micelles.…”