Voltivity (λ): A New Fundamental Material Constant Governing Electric Field-Lattice Coupling in Crystalline Solids

We report the discovery of voltivity (λ), a material constant with units of V·μm that quantifies the threshold for resonant coupling between applied electric fields and phonon modes in crystalline solids. Across 68 experiments spanning 36 materials and 17 crystal structure families, the product of electric field and microstructural interaction length remains invariant for each material (within material coefficient of variation: 1.9%). Values span two orders of magnitude, from ~1,000 V·μm for metals to ~27,000 V·μm for covalent carbides, scaling systematically with bond type. We show λ represents the critical field–length product for coupling electrical work to the universal phonon damping resonance at q^\ast/q_D\approx0.73, where q_D is the Debye wavevector. From a single calibration measurement, λ predicts flash onset conditions at any field strength with errors typically below 3%, providing a practical design tool for field-activated manufacturing. This discovery establishes a new fundamental material property uniting flash sintering, electroplasticity, electromigration, and field-induced phase transformations.