Observation of unusual temperature-dependent stripes in LiTaO3and LiTaxNb1−xO3crystals with near-zero birefringence

A birefringence imaging microscopy study of LiTaO3and some mixed LiTaxNb1−xO3crystals is reported. The initially congruent LiTaO3crystals have been subject to vapour transport equilibration in order to increase the Li content and at the same time to reduce the optical birefringence close to zero at room temperature. In both types of crystal, the presence of unusual periodic self-organized stripes, existing over large distances, has been observed, which correlate with the well documented cleavage and twin planes in this material. Furthermore, the stripes become narrower as the temperature is changed away from the zero-birefringence temperature, but become temperature-independent above the ferroelectric–paraelectric phase-transition temperature.

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Spontaneous strain in synthetic titanite, CaTiOSiO4

Mineralogical Magazine ◽

10.1180/0026461016560002 ◽

2001 ◽

Vol 65 (6) ◽

pp. 709-715 ◽

Cited By ~ 12

Author(s):

T. Malcherek

Keyword(s):

Phase Transition ◽

Room Temperature ◽

Finite Strain ◽

Paraelectric Phase ◽

Strain Tensor ◽

Strain Component ◽

Volume Strain ◽

Single Crystal Diffraction ◽

Paraelectric Phase Transition ◽

Strain Coupling

AbstractLattice parameters of synthetic titanite powder, CaTiOSiO4, have been determined between room temperature and 1023 K. Only the e11 and e13 components contribute significantly to the strain tensor associated with the antiferroelectric-paraelectric phase transition at Tc = 487 K. A finite strain component e13 is observed in the paraelectric phase for 487 K < T < 825 K. The disappearance of this shear strain marks the isosymmetric transition near 825 K. The temperature evolution of the volume strain and of e11 is proportional to the squared order parameter observed in single-crystal diffraction experiments. The magnitude of the volume strain is sufficiently large to relate the observed near tricritical behaviour of the antiferroelectric-paraelectric phase transition to strain coupling.

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Temperature-dependent neutron powder diffraction evidence for splitting of the cationic sites in ferroelectric PbHf0.4Ti0.6O3

Acta Crystallographica Section B Structural Science ◽

10.1107/s0108768198005758 ◽

1999 ◽

Vol 55 (1) ◽

pp. 8-16 ◽

Cited By ~ 20

Author(s):

C. Muller ◽

J.-L. Baudour ◽

V. Madigou ◽

F. Bouree ◽

J.-M. Kiat ◽

...

Keyword(s):

Powder Diffraction ◽

Paraelectric Phase ◽

Neutron Powder Diffraction ◽

Cubic Phase ◽

Temperature Dependent ◽

Paraelectric Phase Transition ◽

Type Method ◽

Space Group ◽

Atomic Displacements ◽

The Mean

Temperature-dependent neutron powder diffraction experiments (diffractometer 3T2-LLB, Saclay, France, λ = 1.227 Å) have been performed on the perovskite-like lead hafnate titanate PbHf0.4Ti0.6O3. This compound belongs to the solid solution denoted PHT, which derives from the well known ferroelectric PZT series. It exhibits a ferroelectric-to-paraelectric phase transition around 620 K, between the low-temperature tetragonal phase and the high-temperature cubic phase. The tetragonal structure of the ferroelectric phase has been refined at 10 and 300 K using a Rietveld-type method: space group P4mm with Z = 1; at = 3.999 (1), ct = 4.120 (1) Å, c/a = 1.030, V = 65.89 Å3 at 10 K; at = 4.012 (1) and ct = 4.100 (1) Å, c/a = 1.022, V = 65.99 Å3 at 300 K. The cubic structure of the paraelectric phase has also been refined at 720 K: space group Pm3¯m, Z = 1, ac = 4.046 (1) Å, V = 66.23 Å3. Cation displacements and oxygen-octahedra elongations have been observed as a function of temperature. Evidence for peculiar behaviour associated with the relative shifts of the Hf and Ti atoms (thought until now to be on the same crystallographic site) was found through an anomaly of the mean-square atomic displacements of the Hf/Ti pseudo-nucleus. The PDF Nos for PbHf0.4Ti0.6O3 are 48-49-9 and 48-49-10.

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