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Subject: search.filters.subject.alkali titanate

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    Item type:Publication,
    Modifying Layered Structure of Alkali Titanates via Vibratory Milling Technique
    (2021-01-01)
    Maluangnont, T.
    ;
    Vittayakorn, W.
    In this work, the layered structure of lepidocrocite-type alkali titanates was modified via the vibratory milling technique. The Cs<inf>2</inf>Ti<inf>6</inf>O<inf>13</inf>, Cs<inf>0.7</inf>Zn<inf>0.35</inf>Ti<inf>1.65</inf>O<inf>4</inf> and K<inf>0.8</inf>Zn<inf>0.4</inf>Ti<inf>1.6</inf>O<inf>4</inf> systems were prepared by calcining the mixed oxide/(hydrogen)carbonate at 800 °C for 20 h with a heating rate of 10 °C/min and a cooling rate of 20 °C/min. After that, these powders were re-milled by vibratory milling for various times in order to study the effect of post-synthetic mechanical milling to structural modification and interlayer spacing. The phase formation of all powders was determined by using X-ray diffractometer (XRD). Lattice parameters and interlayer spacing of all samples were calculated from XRD peaks. The results showed that the single-phase of lepidocrocite-type Cs<inf>2</inf>Ti<inf>6</inf>O<inf>13</inf> and Cs<inf>0.7</inf>Zn<inf>0.35</inf>Ti<inf>1.65</inf>O<inf>4</inf> was maintained after milling, and the interlayer distance increased by 0.5%. Meanwhile, a mixture of expanded- and original one was observed for K<inf>0.8</inf>Zn<inf>0.4</inf>Ti<inf>1.6</inf>O<inf>4</inf>, with the interlayer expansion up to 1.4%. When compared three systems together which had different interlayer ions and alkali-to-titanium ratio, it was found that the interlayer distances of the Cs<inf>2</inf>Ti<inf>6</inf>O<inf>13</inf> (Cs/Ti = 0.33) and Cs<inf>0.7</inf>Zn<inf>0.35</inf>Ti<inf>1.65</inf>O<inf>4</inf> (Cs/Ti = 0.42) systems were not different because the relatively large Cs ion placed itself at the interlayer position. For the K<inf>0.8</inf>Zn<inf>0.4</inf>Ti<inf>1.6</inf>O<inf>4</inf> system (K/Ti = 0.50), the interlayer distance was much lower than those of the Cs<inf>2</inf>Ti<inf>6</inf>O<inf>13</inf> and Cs<inf>0.7</inf>Zn<inf>0.35</inf>Ti<inf>1.65</inf>O<inf>4</inf> because of the smaller K ion.
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    Giant dielectric constants in K0.8M0.4Ti1.6O4 (M = Ni, Zn) lepidocrocite-type layered titanate ceramics
    (2019-01-02)
    Maluangnont, Tosapol
    ;
    Vittayakorn, Naratip
    We reported herein the temperature-dependent dielectric properties of K<inf>0.8</inf>M<inf>0.4</inf>Ti<inf>1.6</inf>O<inf>4</inf> (M = Ni, Zn) lepidocrocite titanate ceramics at the frequency f of 10<sup>3</sup>, 10<sup>4</sup> and 10<sup>5</sup> Hz. This titanate is an example of layered alkali titanium oxides possessing two-dimensional (2D) sheets of edge-shared TiO<inf>6</inf> octahedra, in contrast to other widely studied materials with mostly corner-shared TiO<inf>6</inf> motifs. The giant dielectric constants ε′ ∼10<sup>4</sup> and the dielectric losses tan δ ∼ 0.5–2 were obtained upon heating from RT to 250 °C. These values in our water-free ceramics are comparable to those previously reported in lepidocrocite titanate and related structures containing up to 15%wt water. The results were explained considering (i) Maxwell-Wagner polarization of interlayer species, and (ii) the possible formation of internal barrier layer capacitors (IBLCs) via the oxidized surfaces.