Abnormal temperature dependence of elastic properties of cuprates   superconductors
  In cuprates superconductors (as polycrystal and single crystal samples) unusual hysteretic temperature behavior of elastic properties is frequently observed. In this work from the uniform point of view detailed analysis this abnormal temperature behavior of elastic properties is given. It is shown that the hysteretic temperature dependencies of elastic properties of YBa$_2$Cu$_3$O$_{7-\delta}$ crystal are strongly anisotropic and are connected to hysteretic behavior of the $C_{3333}$ modulus while the $C_{1111}$ and $C_{2222}$ moduli have no such dependence. The analysis of the elastic constant tensor on the basis of the microscopic model has allowed to draw a conclusion, that the hysteretic behavior of the $C_{3333}$ modulus of YBa$_2$Cu$_3$O$_{7-\delta}$ crystal is caused by temperature dependent renormalization of constants of interaction of apex oxygen atoms with copper atoms and are connected apparently to formation of charge ordering. 
Vasilii Gusakov