A Mixed Alkali Metal Titanate with the Lepidocrocite-like Layered Structure. Preparation, Crystal Structure, Protonic Form, and Acid−Base Intercalation Properties

Abstract

A mixed alkali metal titanate of composition A x Ti 2-x/3 Li x/3 O 4 (A ) K, Rb, Cs) has been prepared and its ion-exchange/intercalation properties have been explored. Solid-state calcination of appropriate mixtures of TiO 2 and alkali metal carbonates produced the titanate at a stoichiometry of x ) 0.80 for A ) K, 0.75 for Rb, and 0.70 for Cs. Rietveld refinement on neutron diffraction data confirmed that the orthorhombic structure is comprised of lepidocrocite-related host layers of Ti 2-x/3 Li x/3 O 4 and charge-balancing A ions in the interlayer domain. Complete extraction of both alkali metal ions was achieved by acid-leaching, producing a new protonic titanate of H 4x/3 Ti 2-x/3 O 4 ‚H 2 O. This phase is distinguished from isomorphous related compounds in terms of high proton content as a consequence of exchangeable Li ions located in the host framework. The material took up alkali metal ions and organoammonium ions from aqueous media. These ion-exchange and intercalation reactions brought about expansion/contraction of the gallery height and lateral displacement of the layers. The resulting various types of layer sequence can be understood in terms of the nature of the interlayer species.

Lepidocrocite-type Layered Titanate Structures: New Lithium and Sodium Ion Intercalation Anode Materials

“…15 The interlayer Also listed in Table 1 is another parameter related to structure, that of the charge density.…”

“…They comprise a large class of isomorphous compounds with composition A x Ti 2-y M y O 4 , where A= K, Rb, or Cs, and M represents a vacancy or Li, Mg, Co, Ni, Cu, Zn, or Mn. 15,16,17,18 Lepidocrocite titanates usually crystallize in an orthorhombic structure, consisting of two-dimensional layers of edge and corner sharing octahedra with the large alkali metal ions (A) located in the interlayers. These compensate for the negative charges that arise from the substitution of low valency metal ions or vacancies (M) for Ti 4+ .…”

“…In addition, the interlayer ions in the lepidocrocite structure are highly exchangeable with a variety of inorganic and organic cations. 15,19,20 The compositional flexibility and the capability of using low temperature ion exchange methods mean that a variety of compounds with the desired intercalation characteristics can easily be designed.…”

Electronic Structure of Titania Nanosheets with Vacancies Based on First-Principles Calculations

“…The chemical formula of TNS is known to be Ti 0.87 O 2 , which is synthesized by the delamination from a lepidocrocite-type parent layered K 0.8 Ti 1.73 Li 0.27 O 4 crystal [4]. Thus, the presence of 13 % Ti vacancies is expected.…”

Synthesis and Characterization of Low Loss Dielectric Ceramics Prepared from Composite of Titanate Nanosheets with Barium Ions

“…They have an orthorhombic layered structure that is composed of corrugated host layers of edgeshared octahedra and interlayer (tetramethyl)ammonium ions (TMA + ) compensating for the negative charge which arises from substitution of lower valence metal ions or vacancies of Ti [16]. These TMA + ions are exchangeable with a variety of inorganic and organic ions and in this way the TN is an ideal candidate for host-guest chemistry as well as ion exchange [17].…”