Beyond soft chemistry – bulk and surface modifications of polycrystalline lepidocrocite titanate induced by post-synthesis thermal treatment

Abstract

While the soft chemistry of layered alkali metal oxides is adequately understood, the effect of the post-synthesis thermal treatment on their structure, composition, and properties has been underexplored. In this article, we thoroughly investigated the bulk and surface modifications of KMTiO (M = Ni, Cu, Zn) lepidocrocite titanate thermally treated within 200 °C above its synthetic temperature under air. This practice was typically employed in e.g., specimen fabrication for physical property measurements. We observed the expansion of the interlayer distance (b/2) accompanied by a reduction in layer charge density. These findings can be explained by the deintercalation of interlayer K ions and the loss of intralayer Ti, M, and O species. Meanwhile, the enrichment of potassium and carbonate on the surfaces was evident. The slight differences in dielectric properties of the pellets thermally treated at different temperatures were attributed to the combination of bulk and surface modifications. At 10 Hz and RT-250 °C, the maximum dielectric constants ε' of ∼10 with the dielectric loss (tan δ) ∼0.9-1.5 were obtained for KZnTiO.

Ti0.8O2Nanosheets Inhibit Lung Cancer Stem Cells by Inducing Production of Superoxide Anion

“…Fig. 1B are characteristic of compounds with a lepidocrocite structure, (Sasaki and Watanabe, 1998;Maluangnont et al, 2016Maluangnont et al, , 2017, thereby confirming a successful synthesis. As shown in Fig.…”

Effect of Adsorbed Water and Temperature on the Universal Power Law Behavior of Lepidocrocite-Type Alkali Titanate Ceramics

“…As shown in Figure 4a,c,e, ε′(T) increases with the temperature; this is because the dipole movement is thermally activated. 11,14,31 The dielectric response of the alkali titanates is commonly attributed to the Maxwell−Wagner interfacial polarization 7,30,48 of permanent/ induced dipoles, including electrons/holes, oxygen vacancies, and interlayer ions, to dielectric boundaries. It is found that ε′(T) decreases with increasing f and reaches a maximum value of ∼250,000 (10 2 Hz), ∼20,000 (10 4 Hz), and ∼2000 (10 6 Hz) at 400 °C.…”

“…The capacitance of the specimen was collected during such temperature scans in both directions. The dielectric properties were then calculated from the measured capacitance using the parallel plate capacitor model and the dimensions of the pellet. , In frequency scan experiments, the pretreated pellet was similarly heated to 400 °C and cooled down to/stabilized at the target temperature for 15 min prior to the measurement.…”

“…19−22 In particular, the layered alkali titanates can undergo exfoliation into nanosheets, 23 which are an important component in nanoelectronics 24 or triboelectric nanogenerators. 25−27 In these cases, water can be incorporated either as (i) crystalline hydrates at the interlayer space, 28,29 (ii) noncrystalline hydrates at the grain boundary/porosity/ external surfaces, 11,30,31 or (iii) the combination of these two. 7,32 Investigating the effects of noncrystalline water will widen our fundamental understanding of water-induced conductions, complementing extensive works on the crystalline hydrated (i.e., protonic) titanates 1,28,33,34 analogues, 2,35 offering ways to enhance the sensing performances, and so on.…”

“…It is well known that alkali-containing ceramics are prone to atmospheric water adsorption. Among these, several members of the alkali titanate family have received increasing attention thanks to their superionic conduction, giant/colossal dielectric permittivity, ,, and water-induced transport properties. − The alkali titanates show rich structural chemistry and compositional flexibility, as exemplified by the layered or tunnel-structured Andersson–Wadsley-type A 2 O· n TiO 2 (A = alkali; 1 ≤ n ≤ 6) and the lepidocrocite-type layered A x Ti 2– y M y O 4 (M = transition metals of the first row). − In particular, the layered alkali titanates can undergo exfoliation into nanosheets, which are an important component in nanoelectronics or triboelectric nanogenerators. − In these cases, water can be incorporated either as (i) crystalline hydrates at the interlayer space, , (ii) noncrystalline hydrates at the grain boundary/porosity/external surfaces, ,, or (iii) the combination of these two. , Investigating the effects of noncrystalline water will widen our fundamental understanding of water-induced conductions, complementing extensive works on the crystalline hydrated (i.e., protonic) titanates ,,, and the nanosheet analogues, , offering ways to enhance the sensing performances, and so on.…”