Hi, you are having a phase transitions.

I attach an article where you can spot the different position of the diffraction peaks for the different phases of alumina!

X-ray diffraction (XRD) is a powerful analytical technique used to study the crystal structure of materials. When a material is subjected to high temperature, it can undergo various changes in its crystal structure, which can be reflected in its XRD pattern.

Al2O3, also known as aluminum oxide, is a commonly used material in many industries due to its high melting point, excellent thermal stability, and good electrical insulating properties. When Al2O3 is heated to 1000°C, it undergoes a phase transformation from alpha-Al2O3 to gamma-Al2O3.

The crystal structure of alpha-Al2O3 is rhombohedral, while gamma-Al2O3 has a cubic crystal structure. This change in crystal structure results in a change in the XRD pattern of the material.

Before heating, the XRD pattern of Al2O3 typically shows sharp peaks corresponding to the rhombohedral crystal structure of alpha-Al2O3. After heating to 1000°C, the XRD pattern shows broader peaks corresponding to the cubic crystal structure of gamma-Al2O3.

Therefore, the XRD pattern of Al2O3 changes before and after heating to 1000°C due to the phase transformation from alpha-Al2O3 to gamma-Al2O3.

Alireza Badiei thank you sir, I appreciate you so much.

David Nieto Castro thank you, I'm so grateful for your answer

I would be happy to help you understand why the XRD pattern of Al2O3 changed after heating.

Firstly, it is important to note that heating Al2O3 to 1000°C may cause it to lose some impurities such as water and other volatile substances that were initially present in the sample. This could potentially affect the XRD pattern and cause changes in the diffraction peaks observed.

However, it is also possible that the changes in the XRD pattern could be due to a phase transformation in the crystal structure of Al2O3. At high temperatures, it is known that Al2O3 can undergo a phase transformation from its initial alpha-phase to a more stable gamma-phase. The gamma-phase has a different crystal structure compared to the alpha-phase and shows different diffraction peaks in the XRD pattern.

In summary, it is possible that the changes in the XRD pattern of Al2O3 after heating could be due to a loss of impurities as well as a phase transformation from alpha to gamma phase. I would recommend further analysis and experimentation to determine the root cause of this change in the XRD pattern.