{"knowledge_schema": {"broad_category": "Materials Science \u2192 Crystallography \u2192 Crystal Systems", "refinement": "This problem focuses on the properties of crystal systems, specifically their ability to exhibit piezoelectricity and ferroelectricity.", "specific_scope": "The task is to identify which specific crystal system allows for piezoelectricity without exhibiting ferroelectricity among the given options.", "goal": "Determine the correct crystal system that meets the criteria of allowing piezoelectricity but not ferroelectricity."}, "summary": "This question pertains to the study of crystal systems in materials science, particularly their electrical properties. The goal is to identify which crystal system can exhibit piezoelectricity without showing ferroelectricity. Among the options provided, the trigonal crystal system is the correct answer, as it allows for piezoelectric effects while not being ferroelectric."}