The Isothermal and Non-Isothermal Growth Behaviors of Ca2Nb2O7 in Molten Slag

Calcium pyroniobate (Ca₂Nb₂O₇) as a kind of lead-free piezoelectric material has been applied for different fields, but the study of isothermal and non-isothermal growth behaviors of Ca₂Nb₂O₇ in the molten slag is infrequent. In this paper, the in situ thermal analyzer with a single hot thermocouple technique (SHTT) is used to study the growth behaviors of Ca₂Nb₂O₇ in molten slag. In the isothermal temperatures, the Ca₂Nb₂O₇ presents two kinds of growth morphology, including three dimensional (3D) rhombus growth and fibrous one dimensional (1D) growth. The 3D rhombus is grown under the range of 1608 to 1628 K. When the temperature further decreases to 1593 K, the growth behavior of Ca₂Nb₂O₇ becomes fibrous in 1D. Growth velocity affected by the degree of supercooling may account for the phenomenon of two kinds of growth behaviors in different temperatures. In the non-isothermal growth process, the cooling rate over 10 K min⁻¹ contributes to multiple crystal nucleuses growth of Ca₂Nb₂O₇. The cooling rate below 5 K min⁻¹ leads to single nuclear growth. This paper provides a control guideline for Ca₂Nb₂O₇ growth.