Generalized Pippard Equations

The Pippard equations for α, CP, and βT near a λ-point transition have been generalized in terms of stress—strain variables. The resulting equations, which interrelate αi, sijT, and CP near a λ point, are tested with data on quartz near its α—β transition. A consequence of the new equations is the prediction that C′=(c11–c12)/2 should be constant for cubic crystals near a λ point; this prediction is compared with experimental data on ammonium chloride.