Ferroelectric‐like phase transition at about 320 K and crystal growth of tungsten‐bronze‐type Na13Nb35O94

摘要

The atomic coordinates of tungsten‐bronze‐type Na13Nb35O94, determined by Craig and Stephenson J. Solid State Chem.3, 89 (1971), are characteristic of one‐dimensional ferroelectric crystals. The transition temperature from the ferroelectric‐like to the hypothetical paraelectric phase is predicted to be about 340 K, on the basis of these room‐temperature atomic coordinates. Calorimetric and dilatometric measurements indicate a gradual transition that is complete on heating by about 320 K. Dielectric permittivity and loss measurements exhibit broad but minor anomalies at about 340 K over the frequency range 0.4–100 kHz. The dielectric loss at 10 kHz is very low, at 0.0035. The spontaneous polarization is predicted to be about 0.3 C m−2. Crystals with maximum dimensions of 2 cm in diameter by 5 cm in length along thecaxis have been grown.