Piezoelectric substrate, piezoelectric element, liquid discharge head and liquid discharge apparatus

A piezoelectric substrate of a perovskite-type oxide is expressed by a general formula of ABO3 having a laminate structure of a single crystal structure or a uniaxial crystal structure expressed by (Pb1-xMx)xm(ZryTi1-y)O3 (where M represents an element selected from La, Ca, Ba, Sr, Bi, Sb and W). The laminate structure has a first crystal phase layer having a crystal structure selected from a tetragonal structure, a rhombohedral structure, a pseudocubic structure and a monoclinic structure, a second crystal phase layer having a crystal structure different from the crystal structure of said first crystal phase layer and a boundary layer arranged between the first crystal phase layer and the second crystal phase layer with a crystal structure gradually changing in a thickness direction of the layer. The thicknesses of the first and second crystal phase layer differ.