A comparison is made between the first-order transitions that occur in ferroelectric BaTiO3, metastable NiS, and superconductive La1.85Sr0.15CuO4. In BaTiO3, the cation subarray is cooperatively displaced relative to the anion subarray below a ferroelectric Curie temperature Tc ; in NiS, if quenched from high temperature to retain the B81 nickel-arsenide structure, a dilatation of the lattice marks an anti-ferromagnetic ordering below a Néel temperature TN as well as a semiconductor-metal transition. In the mixed-valent compound La1.85Sr0.15CuO4, there appears to be a dynamic disproportionation into antiferromagnetic spin fluctuations and superconductive regions below a critical temperature Tc . The importance of a first-order change in the ionic/covalent component of the metal-nonmetal bonding in each case is discussed.
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John B. Goodenough (1992) studied this question.
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