Continuous c-oriented AlPO₄-5 films by tertiary growth

c-Oriented AlPO₄-5 films were synthesized by seeded growth on silicon substrates. Secondary hydrothermal treatment of the seeded substrates under conditions that favor c-out-of-plane growth yielded non-intergrown, highly oriented columnar crystals with a length of 7 μm. Modifying the conditions so that in-plane growth is favored and executing yet another ("tertiary") growth, the crystals obtained by secondary treatment were grown in-plane, along the a-, b-directions, filling the gaps between the columnar grains and yielding well-intergrown, highly oriented, continuous AlPO₄-5 films. The oriented films obtained by the technique presented here can be potentially useful for separations and catalysis as well as electronic and electrochemical applications.