Yes, it is relatively common for PhD students to change their research topic during the course of their PhD studies. The reasons for changing research topics can vary depending on individual circumstances, research progress, and evolving interests. Some common reasons why PhD students may change their research topic include:

Evolving research interests: As PhD students progress in their research and gain a deeper understanding of their field, their interests may evolve. They may discover new research areas or develop a stronger passion for a different topic, leading them to change their research topic to align better with their evolving interests.

Lack of progress or challenges: PhD research can be complex and challenging, and sometimes students may encounter difficulties or lack progress in their initial research topic. This could be due to various reasons such as technical limitations, resource constraints, or unforeseen challenges. In such cases, changing the research topic may be necessary to overcome the obstacles and make progress.

Opportunities for collaboration or funding: PhD students may also change their research topic based on new opportunities for collaboration or funding. For example, if a student receives a research grant or collaboration opportunity in a different research area, they may need to change their research topic to align with the new opportunity and secure funding or collaboration support.

Supervisor or lab expertise: PhD students often work closely with their supervisors and research labs, and their research topic may be influenced by the expertise and resources available in their lab or with their supervisor. If there are changes in the expertise or research focus of the supervisor or lab, it may prompt a change in the research topic for the student to align with the new direction.

Interdisciplinary research: Interdisciplinary research is becoming increasingly popular, and PhD students may change their research topic to pursue interdisciplinary research opportunities. This could involve exploring new areas of research that intersect with their field or collaborating with researchers from different disciplines, which may require a change in research topic to accommodate the interdisciplinary nature of the research.

It's important to note that changing research topics during a PhD is not uncommon and can be a part of the research process. However, it typically involves careful consideration, consultation with advisors, and adherence to the requirements and regulations of the PhD program and institution.