The ligand field diagram for octahedral complex is explained here.
In a free metal ion, all the five d-orbitals are degenerate (i.e, having equal energies). But according to crystal field theory, under the influence of ligand field, degenracy of d-orbital is destroyed and they split into two or more energy levels. The difference in energy between two sets of d-orbitals is called Crystal Field Splitting Energy (CFSE). The extent of splitting depends upon the strength of ligand. A strong ligand causes greater splitting whereas weak ligand causes smaller splitting.
In octahedral complex, under the influence of ligand field, degenerate five d-orbitals split into two sets of orbitals -one is [tex]t_{2g}[/tex] and another one is [tex]e_{g}[/tex]. [tex]t_{2g}[/tex] orbital consists of [tex]d_{xy} , d_{xz} , d_{yz}[/tex] and [tex]e_{g}[/tex] orbital consists of [tex]d_{x^{2}-y^{2} } and d_{z^{2} }[/tex] orbitals.
The crystal field splitting diagram for octahedral complex is attached here.
In the diagram, Δo is crystal field splitting energy (CFSE).
