Some piezoelectric materials are sensitive to stress and some to strain. How can I recognize these two groups?
PZT is the best one. And there are also Quartz, Rochelle salt, Barium titanate, PVDF. I cannot understand well your question by saying sensitive to stress and strain. Are they not the same? Because as long as we apply a stress, it will then cause the strain, and to produce the voltage.
Murata produces such piezoelectric devices; you can try to download their catalog section and you can find there some examples of piezoelectric senzitive devices.
Stress (e.g. due to pressure, compression) will induce strain in the material. This strain will thus change the material electrical properties, mostly when you consider semiconductors, insulators/ceramics. Then depending on the kind of materials, you can generate a change in resistance (piezoresistance) or generate a voltage difference (piezoelectricity). Silicon is among the most used in piezoresistance, while PZT, ZnO and GaN are used for their piezoelectrical properties. Note that at nanoscale those properties can be enhanced. Have a look at www.piezonems.com
if we talk about PZT (say), it may function in active (resonator) mode and passive (receiver) mode depending on its dopant composition. Adding Nb makes PZT soft and it behaves as a sensor and used in strain sensitive devices. On the other end, Sr doped PZT behaves like actuator and produces stress under applied electric field and used in utrasonic devices.
To answer the question directly as asked, the word 'piezoelectric' means that it produces electricity as a result of pressure (i.e. stress). Like any material, piezoelectric materials have a stress-strain curve, so any stress causes strain and vice versa. In other words, you are talking about one type of materials, not two.
Thanks all of you for your answer,i have one question,all stress in materials make strain?i think no,in some materials in a range by applied force no strain but curve of resistive-strain show changes.why?
Yes, all materials have a stress-strain curve and a Young modulus, as indicated here. In the elastic region the relation is stress=E*strain, where E is the YOung's modulus. Soft materials have a low Young modulus, hard materials have a high modulus, but all materials have a Young's modulus that controls deformation in the elastic region. Stress is usually denoted by the Greek letter sigma and strain by the Greek letter epsilon. Stress is defined as the force divided by the area on which it is applied and strain is the elongation divided by the initial length (in tension).( These are basic terms that one is expected to know before dealing with piezoelectric materials)...
Thanks for your answers but how about in creep position why in this case the curve of resistive-strain change?
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