Self-organized nanoporous systems produced by using electrochemical processes have in the past decade attracted much interest owing to remarkable potential applications, for example, in high-density recording media, biological nanopatterning, optical devices, functional electrodes, and templates for nanoscale materials. Now, materials that exhibit self-organized anodic pore or tube growth include not only the wellstudied cases of aluminum oxide [1][2][3][4] and silicon [5][6][7] but a variety of metals and compounds. In our group, the fabrication of self-organized oxide nanotubes on valve metals has been investigated for titanium oxide, [8][9][10][11][12][13] zirconium oxide, [14,15] hafnium oxide, [16] niobium oxide, [17] tungsten oxide, [18] and tantalum oxide. [19] In these experiments, comparably thick layers consisting of oxide nanotubes with a diameter of ca. 20-100 nm were synthesized by anodizing metals in fluoride-ion-containing electrolytes. Oxide nanotubes grow as a result of a competition between electrochemical oxide formation and chemical dissolution of oxide by fluoride ions. In order to extend the functionality of the tubular materials by a new composition of oxides, one may target not only to produce binary oxide nanotubes but multicomponent oxide tubes by anodization of multielement alloys.[20] However, considerable difficulties can exist such as preferential dissolution due to chemical inhomogeneousness in the case of multiphase alloys. [20] In the present work, we demonstrate the direct formation of zirconium titanate (ZT) nanotube layers on a single phase Ti-Zr alloy. ZT is used as microwave resonant components and frequency-stable oscillators, [21][22][23] optical devices, [24,25] refractory ceramics, [26] and as a template for lead ZT (PZT). The Ti-Zr alloy system shows a solid solution behavior over the entire composition range.[27] This is particularly interesting as ZT complex oxides also show a solid solution behavior in the composition range between about X Ti = 0.4 and 0.7, including the compounds of ZrTiO 4 , Zr 5 Ti 7 O 24 , and ZrTi 2 O 6 . [28][29][30] The present work uses a (NH 4 ) 2 SO 4 + 0.5 wt % NH 4 F electrolyte for the growth of the nanotubular layers, that is, an electrolyte where nanotubes on elemental Ti and Zr could be successfully grown. Figure 1 shows the current density versus potential curve (Fig. 1a) and the current density versus time behavior during potentiostatic anodization at 20 V (vs. Ag/AgCl) (Fig. 1b) for the Ti-Zr alloy in 1 M (NH 4 ) 2 SO 4 + 0.5 wt % NH 4 F solution. During the potential sweep (Fig. 1a), the current first increases up to 7 mA cm -2 and then drops to a steady value of 4.5 mA cm -2 . This behavior has been found for pore formation on several valve metals including titanium [8][9][10][11][12][13] and zirconium. [14,15] In the initial stage with a current increase, an oxide layer is formed, which then becomes perforated and converted to a porous wormlike initial layers (the latter is combined with an increase in the active surface area). W...