Role of Crystallographic Texture and Crystallinity on the Electrochemical Behavior of Nanocrystalline Sr Doped Calcium Phosphate Coatings

In order to decipher the effect of crystallite size and crystallographic texture on the electrochemical properties of strontium doped calcium phosphate (CaP) coatings, electrodeposition was carried out on two different substrates (Ti and NiTi) and at two different current densities (-1.5 and -3.5 mA cm(-2)). X-ray diffraction (XRD) studies confirmed the presence of brushite and hydroxyapatite (HaP) phases in varying weight fraction as an effect of varying current densities. XRD line profile analyses showed crystallite size of both CaP phases decrease with increase in current density. X-ray pole figures revealed preferential orientation (texture) of HaP crystallites in [0001] direction and it is pronounced at higher current density for both substrates. Surface characterization and phase analysis were carried using scanning electron microscopy and transmission electron microscopy (TEM). TEM results corroborate the local texture of HaP crystallites, where arc diffraction pattern of (0002) facet was observed. Polarization studies revealed that coating synthesized at higher current density on NiTi having high degree of texture showed i(corr) of 10(-8) A cm(-2), which is one order less than that of values obtained for other coatings (10(-7) A cm(-2)). Electrochemical impedance spectroscopy studies exhibited two relaxation features, suggesting the formation of inner barrier and outer porous layer. (C) 2016 The Electrochemical Society. All rights reserved.