三压电方程 研究绝热条件,要用热焓:dH= TdS-xidX- Dde d, T= aH/OS,x=-aH/aX, Dm=-OH/OE (13) 另外,将热焓在平衡态附近展开,H=H+(∂H/S)dS (aH/OXidX +(aH/aEmdEm (14) 将TX和Dm看成SX和Em的函数,有 X=(OX/OS)XES+(OX/OXis EX; +(ox /oEmxsE (15) Dm=(O Dm/asxES+( Dm /OXsEX; +(o Dm /oEm)xsEm (16) TEO T aSxES+(O T/OXisEX +(aT/oMx.sEm (17)三.压电方程 研究绝热条件，要用热焓：dH=TdS-xidXi -DmdEm 则，T= H/S, xi=- H/Xi , Dm= -H/Em (13) 另外，将热焓在平衡态附近展开，H=H0+(H/S)dS+ (H/Xi )dXi+ (H/Em)dEm (14) 将T,xi和Dm看成S,Xi和Em的函数，有 xi= (xi /S)X,ES+ (xi /Xi )S,EXi+ (xi /Em)X,SEm (15) Dm= ( Dm /S)X,ES+ ( Dm /Xi )S,EXi+ ( Dm /Em)X,SEm (16) T= ( T /S)X,ES+ ( T /Xi )S,EXi+ ( T /Em)X,SEm (17)