The following examples of phase transitions are discussed either in this chapter or in other parts of the book. In each case, would you describe the transition as reconstructive, displacive, or order–disorder in nature? State whether or not you would expect to be able to isolate the high-temperature phase at low temperature.

(a) The transition from αquartz to β-quartz at 573 °C.

(b) The transitions from β-quartz to tridymite (870 °C) then to β-cristobalite at 1470 °C.

(c) The transition at 641 °C of the a⁰b⁰c⁺ -tilted NaNbO₃ perovskite (P4/mbm) to the cubic (Pm3m) perovskite a⁰b⁰c⁰ . 

(d)