2D companion to the 3D pyroelectric nanogenerator scene: the same physics, read off a live dipole cross-section and two scrolling strip charts instead of a rendered slab. A pyroelectric crystal has a built-in spontaneous polarization P(T) even with no applied field. Unlike the piezoelectric effect, no mechanical strain is needed — only a change in temperature matters.
Short-circuit current: I(t) = A · p(T) · (dT/dt)
Harvested charge: Q = A · ∫ p(T) dT ≈ A·p·ΔT
Curie-Weiss falloff: P(T)/P₀ ≈ 1 − T/T_c, T < T_c
p = pyroelectric coefficient [C/(m²·K)], A = electrode area, T_c = Curie temperature
- Heating (dT/dt > 0): the lattice's random thermal vibration grows, the net dipole moment per unit cell shrinks, bound surface charge is released, and free charge flows from the electrodes to compensate — a real, measurable current with no source of EMF other than the clock on the temperature.
- Cooling (dT/dt < 0): polarization rebuilds and the current reverses direction — this is why the charge markers in the wire loop flip direction every half-cycle.
- Above Tc: the crystal enters the paraelectric phase, dipoles disorder, and P → 0 — no further pyroelectric response is possible until it cools back below Tc. ZnO nanowires are wurtzite and have no true Curie transition, so they stay poled at any practical operating temperature.
- Load resistance sets how quickly accumulated charge bleeds off the electrodes between temperature swings, which is why a higher load smooths the output but a lower one tracks dT/dt more sharply.
Real devices: waste-heat and body-heat energy harvesters, self-powered wireless temperature sensors, and fire/IR detectors (pyroelectric IR sensors use exactly this ΔT-driven charge pulse).