Massive hydration-driven swelling of layered perovskite niobate crystals in aqueous solutions of organo-ammonium bases

Abstract

Osmotic swelling behaviors in layered perovskite niobate were examined in aqueous solutions containing three types of amine-related agents including quaternary ammonium hydroxides and tertiary aminoethanol. Platelet microcrystals of a protonated layered perovskite niobate, HCaNbO·1.5HO, were found to show enormous swelling in the aqueous solutions, which was clearly recognized by the noticeable expansion of the sample volume over 100-fold. Optical microscopy observations revealed that the crystals underwent accordion-like elongation in the layer-stacking direction up to several ten-fold the initial thickness. Small-angle X-ray scattering measurements of swollen samples indicate the expansion of interlayer separation ranging from ∼20 nm to over 100 nm, which is primarily governed by the concentrations of the amine-related agents. The magnitudes of the interlayer separation were comparable to those of the macroscopic swelling. The degree of swelling was progressively suppressed with further increasing concentration, and this suppression trend was related to the amines.

Single-Crystal Growth of Layered Birnessite-Type Manganese Oxides and Their Delamination into MnO2 Nanosheets

“…According to these results, the crystal sizes had a significant dependence on the swelling agents. We have reported similar massive swelling phenomena for lepidocrocite-type titanium oxide H 0.8 [Ti 1.2 Fe 0.8 ]­O 4 ·H 2 O and perovskite-type niobium oxide HCa 2 Nb 3 O 10 ·1.5H 2 O in TMAOH and TBAOH solutions. , Such conspicuous swelling can be ascribed to the penetration of a large volume of water into the interlayer gallery, which promotes the delamination owing to the weakened interlayer interactions.…”

“…28 In the preparation of Ca 2 Nb 3 O 10 − nanosheets, the exfoliation of large platelet crystals of layered niobates has also been studied. As a result, the lateral size of the Ca 2 Nb 3 O 10 − could be controlled to be ∼10 μm 29,30 while that obtained from a polycrystalline sample of layered niobates measured ∼1 μm. Although the single-crystal growth of birnessite-type K x MnO 2 , the mother phase of MnO 2 nanosheets, has been studied, there have been few studies on enlarging the nanosheet size.…”

“…We have reported similar massive swelling phenomena for lepidocrocite-type titanium oxide H 0. 29,30 Such conspicuous swelling can be ascribed to the penetration of a large volume of water into the interlayer gallery, which promotes the delamination owing to the weakened interlayer interactions.…”

Nematic suspension of a microporous layered silicate obtained by forceless spontaneous delamination via repulsive osmotic swelling for casting high-barrier all-inorganic films

“…Layered or two-dimensional (2D) materials represent a versatile tool with a variety of properties. The pronounced anisotropy in bonding strength of layered solids like graphite ( 1 ), clay minerals ( 2 ), transition metal dichalcogenides ( 3 ), lepidocrite-type titanates ( 4 ), perovskite-type niobates ( 5 , 6 ), or NaFeO 2 -typ cathode materials ( 7 ) leads to a platy morphology and, in many cases, to intracrystalline reactivity. The latter is frequently taken advantage of to increase the basal spacing and thus weaken the adhesion between layers.…”

“…Contrary to brute-force liquid-phase exfoliation, nanosheets of some charged layered materials may alternatively be obtained by thermodynamically allowed delamination via so-called repulsive osmotic swelling [see ( 14 ) for a definition of exfoliation versus delamination]. This was, however, long limited to a handful of layered compounds such as titanates ( 15 , 16 ), niobates ( 5 , 6 ), antimonates ( 17 ), manganese oxides ( 18 ), tungsten oxides ( 19 ), and clay minerals ( 20 , 21 ). The process resembles the dissolution of ionic crystals while being limited to one dimension because of the anisotropic bonding situation.…”