The spatial distribution and atomic mobility of Li ions in the solid solution system Li1-xNb1-xWxO3 (0 ≤ x ≤ 0.5) have been studied using solid-state NMR techniques. To maintain charge balance, for each tungsten atom substituting on a niobium site, a lithium vacancy is produced in the lithium sublattice. 6Li magic angle spinning experiments reveal multiple lithium sites, attributed to distributions of niobium and tungsten neighbors. Dipolar 7Li second moments measured at low temperature (−100 °C) depend linearly on lithium content, consistent with a random distribution of vacancies. Variable temperature (−20 to 550 °C) 7Li NMR studies as a function of composition give evidence for two distinct motional processes:  at low temperatures (near 0 °C) a local hopping process involving only a minority of the lithium ions present is activated. At high temperatures (300 °C and above, depending on substitution levels) long-range diffusion involving all the lithium atoms is evident on the NMR time scale. As the subs...

7Li and 6Li Solid-State NMR Studies of Structure and Dynamics in LiNbO3−WO3 Solid Solutions

High-densified LiTaO3-type ceramics have been obtained by sintering at 900°C after the addition of small amounts of a LiF + MgF2 mixture. Partial hydrolysis of MgF2 and volatilization of either LiF, LiOH, or Li2O due to hydrolysis and partial substitution of F-ions by (OH−) occur during heat treatment. The ferroelectric Curie temperature T
c increases with the amount of additive. The ceramics have been polarized by heating to T
c and cooling down under a dc field. The piezoelectric and pyroelectric coefficients of such ceramics are approximately 30% and 20% of the corresponding values for a LiTaO3 single crystal.

Dielectric, piezoelectric, and pyroelectric studies of LiTaO3-derived ceramics sintered at 900°C following the addition of (LiF + MgF2)

The crystallization of amorphous oxides synthesized by pyrolytic decomposition of mixed Li and Ta 2-ethylhexanoates and alkoxides has been investigated. The study was motivated by thermodynamic considerations that, in the light of experience in other systems, suggest the potential for metastable extension of the LiTaO3 homogeneity range. Materials investigated are described by the general stoichiometry Li1−5xTa1+xO3 and include Li2O contents from 0 to 70 mol% (−0.18 ⩽ x ⩽ 0.2). The samples were prepyrolyzed at 400 °C and subsequently crystallized by heat treatments in air at 550–700 °C for 0.1–100 h. The first product of crystallization for compositions from 30 to 65% Li2O is always the LiTaO3 phase. Extensive characterization by x-ray and neutron diffraction, as well as 7Li-NMR spectroscopy, revealed that this phase evolves with a structure and stoichiometry close to equilibrium. For Li+-deficient compositions, excess Ta5+ is rejected to the amorphous constituent during crystallization and eventually gives rise to the evolution of Ta2O5, with the LiTa3O8 phase suppressed in all cases. Similar observations were made for the Li+-rich compositions, but the evolving second phase is the equilibrium Li3TaO4. The absence of solubility extension in LiTaO3, which appears feasible from a thermodynamic viewpoint, is ascribed to the large differences in mobilities of the Li and Ta species in the parent amorphous oxide resulting from pyrolysis.

Crystallization behavior of Li 1–5 x Ta 1+x O 3 glasses synthesized from liquid precursors

Electrical properties of Mg-doped LiTaO3 ceramics

Ferroelectric solid solution Li1-xTa1-xWxO3 as potential photocatalysts in microbial fuel cells: Effect of the W content

In order to modulate the properties of LiTaO3 ceramics Li+ or Ta5+ cations have been substituted by mono-, di-, tri-, tetra-, penta- or hexavalent cations A large number of solid solutions have been obtained, the observed nonstoichiometry corresponds either to a cationic excess or to a cationic deficit from LiTaO3 7Li NMR measurements allowed the authors to point out the position of the substituted cations either in the tetrahedral or in the octahedral sites The dependence of the Curie temperature Tc vs composition has been determined The variation of Tc was related to width and intensity of the NMR quadrupole splitting

The Ferroelectric Non-Stoichiometric LiTaO3-Type Phases

Magnesium and zinc cation distributions and correlation with curie temperature in some LiTaO3-based ferroelectric ceramics

Some new phases with a LiTaO3-related structure have been prepared within the ternary system Li2O-Ta2O5-(WO3)2. They are either stoichiometric or non-stoichiometric with cationic excess or deficit with regard to LiTaO3. Each material has a ferroelectric-paraelectric transition. The Curie temperature decreases when the composition deviates from LiTaO3.

Some new non-stoichiometric ferroelectric phases with composition close to LiTaO3 in the ternary system Li2O-Ta2O5-(WO3)2

Preparation des solutions solides (Li 1−x M x/3 3+ )TaO 3 (M=Al, Cr, Fe, In). Detection par mesures dielectriques d'une transition ferroelectrique-paraelectrique. La temperature de Curie decroit avec x et peut etre correlee au rapport c/a de la maille hexagonale

G. T. Joo

Papers

The Ferroelectric Non-Stoichiometric LiTaO3-Type Phases

Magnesium and zinc cation distributions and correlation with curie temperature in some LiTaO3-based ferroelectric ceramics

Some new non-stoichiometric ferroelectric phases with composition close to LiTaO3 in the ternary system Li2O-Ta2O5-(WO3)2

Crystallographic and dielectric properties of LiTaO3-based non-stoichiometric solid solutions substituted by trivalent ions

Ferroelectric properties of oxygen deficient PbTiO3-related phases