Microscopic probing of order-disorder versus displacive behavior in BaTiO3 by Fe3+ EPR

The cubic-crystalline field-splitting parameter a of Fe3+ at a Ti site in BaTiO3 has been measured with EPR in the cubic phase as a function of pressure p and temperature T. From these measurements, the relative explicit volume and temperature dependences of a(p,T) have been obtained. The former is three times those found in MgO, KTaO3, or SrTiO3. The relative explicit temperature dependence( lna/T)V is positive and four and a half times that found in inert MgO. In contrast, this effect is negative in KTaO3 and SrTiO3, where soft underdamped ferroelectric modes dominate. Both giant effects in BaTiO3 point to a strong local Ti anharmonicity and ferroelectric order-disorder behavior in contrast to SrTiO3 and KTaO3. © 1986 The American Physical Society.