Pyroelectric Nanogenerator: Harvesting Energy from ΔT/Δt

Material

Thermal Cycle

Heating / cooling rate 4.0 °C/s

Temperature swing ΔT 60 °C

External load resistance 10 MΩ

Live Readout

Film temperature

25.0 °C

dT/dt

+4.00 °C/s

Pyroelectric current

0.0 nA

Polarization P/P₀

100 %

Harvested charge (this run)

0.0 nC

How it works

A pyroelectric crystal (here PZT/PVDF/ZnO) has a built-in spontaneous polarization P(T) even with no applied field — it is already "poled". 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 flowing charge markers in the wire loop below flip direction every half-cycle.
Above T_c: the crystal enters the paraelectric phase, dipoles disorder (visualized as scattered arrows in the slab), and P → 0 — no further pyroelectric response is possible until it cools back below T_c. 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).

Ferroelectric

Dipole (polarization) Flowing charge

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