Large and stable thickness coupling coefficients of [001]C-oriented KNbO3 and Li-modified (K,Na)NbO3 single crystals

Large thickness coupling factors k(T)<= 0.7 are measured in both [001](C)-oriented (45 degrees cut in the orthorhombic ac plane), monodomain and [001](C)-poled, domain-engineered single crystals of KNbO3. k(T) is extremely stable over a large temperature range, remaining high (>= 0.65) even upon heating and cooling through the orthorhombic-tetragonal phase transition. This is likely related to another finding that spontaneously high k(T) values (<= 0.68) are observed in as-grown (unpoled), [001](C)-cut, polydomain KNbO3 crystals. k(T) is also stable upon thinning to thicknesses below 60 mu m, as required for high-frequency applications. Finally, large k(T) values (<= 0.7) are reported in [001](C)-poled, polydomain, Li-doped (K0.5Na0.5)NbO3. (c) 2007 American Institute of Physics.