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The chara cteri stics of th e di electri c rehtxat ioll spectrum associat ed wi t h some simple three-dimensional la t t ices consisting of polar molecules of specified shape ha ve been investigated with t he object of determining whether dielectri c loss curves with two distin ct m ax ima (bimodal loss curves) could be predicted on a t heoretical bas is for such systelEs. For the ty pes of latt ice and mo lecular shape co nsidered, each dipole has one stable and four m etastable orientat ions. Th e calcula tion s show that under certain circum sta nccs bimodal Joss curves may a ri se fo r pear-shaped molcc ul cs in both th c body-centered or t horhombic and t etragonal systems. All of t he models lead t o a Sin gle loss peak if t h e barrier system is suffi ciently isotropi c as in t he body-cen ter~d cubic lattice. The ch anges wit h temperature of th e shape of t he loss curves, t he static d lClectn c constan t, and t he confi gurational entropy are d iscussed. The a bru pt cha nges in these propert ies t hat will occ ur at phase t rans it ions du e to cooperat ive interact ion are also considered . Qualitative p redictions co nce rning t he ex pected behav ior of bimodal loss curves for t hree-dimensional httt ices, in whi ch each dipole has o nl y a s in gle stable on en tatlOll, a re compared Wit h expel"lment. Usin g a n argum ent based on t he fact t hat broadened loss curves in monophase molecular crystals become narrower wit h inc reasin !!; temperature, it is concluded t hat flu ctuat ions of structure a rc not t he pri ncipal cause of t he broadening of loss curves . Th e presen t t heo ry leads to t he correct type of te mperature dependence, a nd t his strengthens t he view th~t t he origin of m ult ipl e relaxation t imes in molecula r crystals is t he anisotropy of t he crystalline fi eld.

Theory of dielectric relaxation for the three-dimensional polar rotator: Lattice models leading to bimodal loss curves