Which of the following statement about Frankel's defect is incorrect.

Which of the following statement about Frankel's defect is incorrect.
A.空位、填隙原子成对出现，两者数量相等。
B.晶体的体积发生改变。
C.不需要自由表面。
D.正负离子半径相差大时，易形成Frenkel缺陷。
正确答案：晶体的体积发生改变。