Substrates coated with a multi-film functional coating

1. A coated substrate comprising:

a. an undercoating layer deposited over at least a portion of the substrate, wherein said undercoating layer comprises a material having a brookite crystal structure; and

b. a functional coating layer deposited over at least a portion of the undercoating layer, wherein the functional coating layer comprises a material that can be present in more than one crystal structure.

2. The coated substrate of claim 1 , wherein the undercoating layer has a thickness of at least 1 nm.

3. The coated substrate of claim 1 , wherein the material having said brookite crystal structure is tellurium oxide.

4. The coated substrate of claim 1 , wherein the undercoating layer further comprises a dopant.

5. The coated substrate of claim 4 , wherein the dopant is selected from the group consisting of a cation and an anion.

6. The coated substrate of claim 1 , wherein the functional coating layer comprises a photocatalytic coating.

7. The coated substrate of claim 6 , wherein the photocatalytic coating comprises at least one metal oxide or semiconductor metal oxide selected from the group consisting of titanium oxides, iron oxides, tungsten oxides, zinc oxides, tin oxides, zinc/tin oxides, calcium titanium oxides, molybdenum oxides, niobium oxides, vanadium oxide and mixtures thereof.

8. The coated substrate of claim 1 , wherein the functional coating layer further comprises a dopant.

9. The coated substrate of claim 8 , wherein the dopant is selected from the group consisting of a cation and an anion.

10. The coated substrate of claim 1 , wherein the functional coating layer has a deposition thickness of about 10 nm to about 250 nm.

11. The coated substrate of claim 1 , wherein the functional coating layer is a single film comprised of a material having predominantly a first crystal structure.

12. The coated substrate of claim 1 , wherein the functional coating layer is a multi-film functional coating comprised of a first polycrystalline film made up predominantly of material having a first crystal structure and a second polycrystalline film made up predominantly of the same material having a second crystal structure which is different from the first crystal structure.

13. The coated substrate of claim 12 , wherein the first crystal structure is the rutile crystal structure and the second crystal structure is the anatase crystal structure.

14. The coated substrate of claim 1 , wherein the substrate is selected from the group consisting of a polymer, a ceramic and a glass.

15. A coated glass substrate comprising:

a. an undercoating layer deposited on at least a portion of the glass substrate, the undercoating layer comprising a material having a brookite crystal structure selected from tin oxide, germanium dioxide, beta manganese dioxide, chromium (IV) oxide, iridium oxide, osmium (IV) oxide, ruthenium (IV) oxide, tantalum (IV) oxide, niobium (IV) oxide, molybdenum (IV) oxide, tungsten (IV) oxide, lead (IV) oxides and mixtures thereof; and

b. a photocatalytic functional coating deposited on at least a portion of the undercoating comprising a first titania film having a first crystal structure over the undercoating layer and a second titania film having a second crystal structure over the first titania film.

16. An insulating glass unit comprising:

a. a first glass substrate;

b. a second glass substrate, wherein an undercoating layer is deposited on at least a portion of either the first glass substrate or the second glass substrate, wherein said undercoating layer comprises a material having a brookite crystal structure; and

c. a functional coating layer is deposited over at least a portion of the undercoating layer, wherein the functional coating layer comprises a material that can be present in more than one crystal structure.