*2.4. X-ray Diffraction (XRD)*

The formed phases were recognized via the X-ray diffraction technique. The instrument used was Bruker AXS diffractometer (CD8—ADVANCE) with Cu–Ka radiation operating at 40 Kv and ten mA. The diffraction information was listed as 2θ values between 4◦ and 70◦, and the scanning rate was 10◦/min.

#### *2.5. Scanning Electron Microscope (SEM)*

The microstructure of the synthesized glass–ceramic samples was investigated by using a scanning electron microscope (SEM: JEOL, XL30, Philips, Amsterdam, The Netherlands), that operated at an acceleration voltage of 20 kV. The freshly fractured sample was

coated with a layer of gold on the broken surface (to minimize any charging effect) to observe the internal microstructure.

## *2.6. Thermal Expansion Measurement*

In this study, the mechanical dilatometry technique for thermal expansion measurement is applied. In this technique, a sample is heated in an oven, and the specimen ends; displacements are transmitted to a sensor utilizing pushrods. This test is usually functionalized to materials with CTE above 5 × <sup>10</sup><sup>−</sup>6/K (2.8 × <sup>10</sup><sup>−</sup>6/◦F) over the temperature range of −180 to 900 ◦C (−290 to 1650 ◦F). Pushrods are of high-purity alumina type. Alumina systems can extend the temperature range up to 1600 ◦C (2900 ◦F). The instrument used was NETZSCH DIL 402 PC (made in Japan).

### **3. Results and Discussion**
