The compositional homogeneity of nominally LiNb_1−xTa_xO₃ (x = 0.45) single crystals is studied using micro-X-ray fluorescence and high-resolution X-ray diffraction. Highly homogeneous regions are reported with less than 1 % Ta variation over areas as large as 4 × 4 mm² in z-cut specimens. To our knowledge, this represents the most detailed study of homogeneity in lithium niobate tantalate (LNT) solid solutions to date, establishing a quantitative benchmark for future studies. Spectroscopic ellipsometry shows a decreasing refractive index and blue-shift in optical absorption with increasing Ta content, while the dielectric response remains structurally consistent. These investigations establish a quantitative benchmark for selecting compositionally homogeneous LNT crystals suitable for applications such as second-harmonic generation, Raman spectroscopy, piezoresponse force microscopy, and domain wall conductivity.