The phenomenon in which applying stress produces polarization and, conversely, applying an electric field produces deformation. It occurs in crystals without a center of symmetry; quartz and PZT are used in sensors and resonators.
Japanese name: 圧電効果
Piezoelectric effect appears in 1 practice question across 1 topic, including Ceramics and glasses.
Field: Ceramics and glasses
The appearance of charge on the surface of a crystal under stress is the direct piezoelectric effect, and the straining of a crystal under an electric field is the converse effect; the Curie brothers discovered the direct effect in 1880. The size of the effect is expressed by the piezoelectric coefficient d, in pC/N (charge/force), which has the same dimensions as pm/V (displacement/voltage). It is about 2 pC/N for quartz but reaches several hundred pC/N for PZT ceramics, giving a large response usable in both sensors and actuators.
Of the 32 crystal point groups, 21 lack a center of symmetry, and 20 of those show piezoelectricity. Ten of these are polar crystals with spontaneous polarization, which also show pyroelectricity, a change of polarization with temperature. Ferroelectrics are crystals whose spontaneous polarization can be reversed by an electric field. In PZT and BaTiO₃ ceramics, the polarization direction differs from grain to grain, so as made, the piezoelectricity cancels out. Only after poling, in which a strong DC field is applied at high temperature to align the directions, do they become piezoelectric elements.
In PZT (Pb(Zr,Ti)O₃) there is a boundary between tetragonal and rhombohedral phases (the morphotropic phase boundary) near a Zr/Ti ratio of about 52/48, where the polarization direction changes easily and the piezoelectric coefficient is greatest. Polarization is lost above the Curie temperature, so the service temperature is kept well below it, with about half the Curie temperature as a guideline. Because PZT contains lead, lead-free piezoelectric materials such as those based on potassium sodium niobate (KNN) are also being developed.
The direct effect is used in accelerometers, engine knock sensors, ultrasonic reception and igniters. With the converse effect, the displacement is small but the response is fast and the force large, so it is used for precision positioning and fuel injectors. Applying 100 V to an element with d33 = 500 pm/V gives a displacement of about 50 nm, and stacking 100 layers gives about 5 µm. Quartz crystal resonators produce the reference frequencies of watches and electronic devices, and the high-frequency filters of smartphones use surface acoustic wave devices on LiNbO₃ or LiTaO₃ and AlN thin-film resonators.
Answer: B. All ferroelectrics are piezoelectric, but some piezoelectrics, such as quartz, are not ferroelectric
Piezoelectricity is the property of developing polarization under mechanical stress and, conversely, deforming in an electric field; it requires a crystal without a center of symmetry. Ferroelectrics are crystals with a spontaneous polarization whose direction can be reversed by an electric field; they lack a center of symmetry and so are always piezoelectric. Quartz (α-quartz), by contrast, lacks a center of symmetry and is piezoelectric, but has no spontaneous polarization and so is not ferroelectric. In crystals with a center of symmetry, no first-order piezoelectric effect appears however strong the field (electrostriction, proportional to the square of the field, is a separate effect). Ferroelectric ceramics such as PZT and BaTiO₃ are poled to align the polarization before use as piezoelectric elements.
The piezoelectric effect is a change of polarization with stress, while the pyroelectric effect is the appearance of charge as the magnitude of spontaneous polarization changes with temperature. All pyroelectric crystals are also piezoelectric, but some piezoelectric crystals, such as quartz, are not pyroelectric.
They have the same dimensions. Converting C/N = (A·s)/(kg·m/s²) and m/V = m/(kg·m²/(A·s³)) to base units gives A·s³/(kg·m) for both. For the direct effect it reads as charge per force, and for the converse effect as displacement per voltage.
The generated charge leaks away over time through the insulation resistance of the element and circuit. Piezoelectric sensors are therefore suited to measuring changing forces such as vibration and impact. For quasi-static forces, low-leakage quartz is combined with a charge amplifier.
In crystals with a center of symmetry, no first-order piezoelectric effect appears however strong the field (electrostriction, proportional to the square of the field, is a separate effect).
Which statement about the relation between piezoelectricity…Perovskite structure Sintering Transformation toughening Weibull modulus