TENSILE AND COMPRESSIVE EFFECT OF INTRACRYSTALLINE PRESSURE IN SMALL PARTICLES

It is shown that the volume forces of electrostatic interaction of the crystal lattice elements - ions and electrons - result in intracrystalline pressure (IP) which depends on the size of particles and stipulates the size dependence of the unit cell parameters. Analytical expressions are obtained for the IP by the crystal energy and it is shown that the IP can increase or decrease in small particles depending on the crystal structure, i.e. has tensile or compressing action. The results of the theoretical calculations for NaCl and CeO2 give evidence for the compressing effect of IP in small particles of NaCl and for the tensile effect of IP in small particles of CeO2. These results are in good agreements with experimental data of the changes of the unit cell parameters in small particles of NaCl and CeO2.