Thermodynamic and structural properties of sodium lithium niobate solid solutions

Irina Pozdnyakova, Alexandra Navrotsky, Lidia Shilkina, Larisa Reznitchenko

Research output: Contribution to journalArticlepeer-review

41 Scopus citations

Abstract

Thermodynamics of the Na1-xLixNbO3 system is investigated by high-temperature drop-solution calorimetry in molten 3Na2O-4MoO3 solvent at 973 K. Standard molar enthalpies of formation are derived. The estimated heats of transition between hypothetical and stable structures, lithium niobate and perovskite for NaNbO3 and vice versa for LiNbO3 are -6 kJ/mol and -10 kJ/mol, respectively. X-ray diffraction studies at room temperature showed for 0 ≤ x ≤ 0.14 there are three phases based on different ordering of the perovskite type lattice: orthorhombic with a quadrupled reduced perovskite cell at 0 ≤ x ≤ 0.02, orthorhombic with a doubled reduced perovskite cell at 0.015 ≤ x ≤ 0.14, and rhombohedral at 0.08 ≤ x ≤ 0.13. There are two two-phase (morphotropic) regions with coexistence of the two orthorhombic phases at 0.015 ≤ x ≤ 0.02 and with the second orthorhombic phase coexisting with the rhombohedral phase at 0.08 ≤ x ≤ 0.13. A reproducible anomaly in specific heat at ∼600 K, not reported previously, has been observed in pure NaNbO3. Heat-capacity measurements confirm a phase transition at 553 K for 0.07 ≤ x ≤ 0.09. With increasing lithium concentration, a gradual disappearance of high-temperature phase transitions associated with tilting of oxygen octahedra has been observed.

Original languageEnglish (US)
Pages (from-to)379-384
Number of pages6
JournalJournal of the American Ceramic Society
Volume85
Issue number2
DOIs
StatePublished - Feb 2002
Externally publishedYes

ASJC Scopus subject areas

  • Ceramics and Composites
  • Materials Chemistry

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