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  • 11
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
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  • 12
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Enthalpies of drop solution for a suite of substituted pollucites with the compositions CsTixAl1−xSi2O6+0.5x, 0 ≤x≤ 1, which are synthesized using the sol–gel method, have been measured in molten lead borate (2PbO·B2O3) at 701°C. As Ti4+ substitutes for Al3+, the enthalpies of drop solution become less endothermic and show exothermic heats of mixing within the composition range from x= 0.3 to 1. This nonideal mixing behavior is consistent with the trend seen in variation of lattice parameters, and we interpret it to be a result of the short-range order associated with the framework cations Al3+, Si4+, and Ti4+ in the structure. Using enthalpies of drop solution of SiO2, Al2O3, TiO2, and Cs2O, standard molar enthalpies of formation of these phases from their constituent oxides and from the elements are derived for the first time.
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  • 13
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 1683-1689 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structure of the defect perovskite [Pb0.85(D'Alembertian)0.05La0.10]TiO3 was investigated by powder neutron and x-ray diffraction and by specific heat measurements made at various temperatures. Refinement of the structure by the Rietveld technique at 10, 200, and 300 K from time-of-flight powder neutron diffraction data revealed no low temperature transitions from the ferroelectric tetragonal (4mm) phase. On average, the oxygen octahedral framework of the parent compound was not distorted by the incorporation of lanthanum and vacancies, and the ratio of cation displacements along the polar axis was comparable to that observed for pure PbTiO3. However, the material showed a large nonuniform strain that increased with decreasing temperature. As a result, the effective coupling between the uniform tetragonal deformation and cation displacement was reduced. X-ray diffraction and specific heat measurements at 298–1023 K indicated that the ferroelectric m3m→4mm transition was nearly tricritical and took place at 565 K. The diffuse nature of the transition was reflected in a temperature-dependent x-ray profile broadening and anomalous excess specific heat that persisted to ≈775 K, close to the phase transition temperature of pure lead titanate. © 1995 American Institute of Physics.
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  • 14
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Chemistry of materials 5 (1993), S. 1805-1813 
    ISSN: 1520-5002
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 15
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Inorganic chemistry 6 (1967), S. 2119-2121 
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
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  • 16
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Chemistry of materials 7 (1995), S. 1816-1823 
    ISSN: 1520-5002
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 17
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Inorganic chemistry 8 (1969), S. 756-758 
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
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  • 18
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The structure of Cs2ZrSi3O9 synthesized using a sol–gel method was determined from the Rietveld refinement of experimental powder X-ray diffraction data. The refinement confirmed that this compound was isostructural with wadeite: its structure was hexagonal (space group P63/m), and its lattice parameters were a= 7.2303(2) Å and c= 10.2682(4) Å. The aqueous durability of Cs2ZrSi3O9 varied, depending on the solution conditions. In modified leach tests with buffered (pH 7) and unbuffered solutions, the 7-d cesium release rates were 〈1.2 × 10−4 g·(m2·day)−1, which indicated high aqueous durability. However, in unsaturated, unbuffered solutions with a pH of 9–10, the durability was much lower, with 7-d cesium release rates of 2.2 × 10−3 g·(m2·day)−1. The ability of this material to retain cesium in aqueous environments can be explained by its condensed ring structure, in which the size of the channel openings is smaller than the diameter of a Cs+ ion. However, dissolution of the network silicate occurred at high pH, which resulted in the release of cesium.
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  • 19
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The crystal structures for a suite of substituted pollucites with the compositions CsTixAl1–xSi2O6+0.5x, 0 ≤x≤ 1, have been determined from Rietveld analysis of powder synchrotron XRD data. Our results indicate that the pollucite end member (CsAlSi2O6) has a tetragonal structure (space group I41/a), whereas all other compositions are cubic (space group Ia3d). The increased symmetry for the titanium-substituted structures is presumably due to the incorporation of additional O2− anions (needed for compensating the charge imbalance between Ti4+ and Al3+), which effectively holds open the expanded cubic framework. In situ cooling experiments of the substituted phase CsTi0.1Al0.9Si2O6.05 reveal a displacive transformation to the tetragonal structure at ∼230 K. This transformation is tricritical in nature and is analogous to the tetragonal-to-cubic transition in pollucite on heating.
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  • 20
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 86 (2003), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Enthalpies of drop solution in molten 2PbO-B2O3 at 1078 K were measured for glasses along the 2YAlO3-3SiO2 and return ½Y3Al5O12-3SiO2 joins. The onset glass transition temperature increases slightly with increasing silica content and Y/Al. Enthalpies of mixing were calculated on the basis of amorphous end members. Strongly negative heats of mixing support the absence of miscibility gaps except possibly for very high silica content, consistent with experimental phase analyses, which indicate much narrower miscibility gaps compared with the phase diagrams calculated on the basis of previous data and the CALPHAD formalism.
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