Chiral liquid crystal mixtures are an important field of research in the development of these materials. The main advantage of chiral liquid crystal mixtures is their ability to produce an optically active three-dimensional structure. Moreover, 1,3,4-oxadiazoles have been widely used as electron-transporting/hole-blocking materials or emitting layers in electroluminescent diodes and nonlinear optical materials owing to their interesting properties. Here, we investigate the phase transitions in a mixture of a chiral oxadiazole derivative liquid crystal, EOS-12, and a traditional nematic liquid crystal, E7. EOS-12 is miscible with the E7 matrix at all concentrations. The mesomorphic properties of these mixtures were studied using differential scanning calorimetry (DSC), polarised optical microscopy (POM) and digital colourimetry analysis. In addition, the cholesteric pitch is measured using the Grandjean-Cano technique and photophysical studies were performed in solutions and films. Mixtures show polymorphism depending on the concentration and temperature: nematic, chiral nematic, TGBA*, and smectic phases. A temperature-concentration phase diagram was established using POM. Stabilisation of the SmA phase is observed with a greater temperature range than the constituents of the mixture. According to these results, the properties of the mixture can be used to create various material functionalities, depending on the composition of the mixture.