A method for forming a porous barrier coating on a substrate without substantial chemical segregation includes the steps of providing or obtaining a barrier coating material in powdered form and spraying the barrier coating material onto the substrate using air plasma spraying. The air plasma spraying is performed using an average homologous surface temperature of the depositing particles in a range of about 1.25 to about 1.5 and a particle velocity in a range of about 300 m/s to about 500 m/s. The depositing particles are fully molten.