Pressure-induced enhancement of piezoelectricity of quartz-like single crystals

The piezoelectricity of same material is often affected by its form (such as bulk single crystals, low dimension materials, extension thin film and so on), pressure, stress and strain. In this paper, by first-principles calculation, the piezoelectricity of quartz-like crystals (synthetic quartz, AlPO₄, GaPO₄, GaAsO₄ and GeO₂) was investigated with virtual isostatic pressing. The virtual negative pressure makes its structure close to high temperature quartz phase with a higher symmetry, which lead to first-order phase transition and normal piezoelectric strain coefficient along a-axis disappearing eventually. The piezoelectricity is related closely with tetrahedral tilt angle which is used for characterizing the degree to divergence of centrosymmetry. Uniaxial stress or other non-isostatic pressing can also lead to this kind of increasing or declining, which is a general phenomenon. For a specific type of structure, piezoelectric coefficient can be represented as a simple function of pressure or order parameter. Furthermore, the contribution of piezoelectric effect can be divided into two parts, clamping ion and internal strain contribution. Then the internal strain is divided to each cell to get microscopic piezoelectric coefficient of every ions and oxygen tetrahedrons. By compared variation of tetrahedral tilt angle and microscopic piezoelectric coefficient of these five kinds of crystals, we get an explanation of the relationship between structure parameters and piezoelectric effect of quartz-like crystals in microcosmic level.