Polymorphism and piezoelectricity of glycine nano-crystals grown inside alumina nano-pores

Glycine nano-crystals were grown inside alumina nano-pores due to a precipitation process from over-saturated aqueous liquid solutions. The α-glycine polymorph crystals were formed at a higher over-saturation concentration than that of the β-glycine polymorph crystals. The results indicate that the type of the glycine polymorph formed inside the alumina pores is kinetically controlled. A model is suggested to explain the competition between formations of the two polymorphs inside nano-pores. The β-glycine polymorph crystals are distinguished from the α-glycine polymorph crystals not only by XRD measurements but mainly by piezoelectric measurements, where only the non-centro-symmetric β-glycine polymorph crystals show a piezoelectric current response to applied mechanical pressures as low as 1 Pa in the environmental pressure of 1 atm (10–3% pressure change).