Liquid-crystalline medium

A liquid-crystalline medium based on a mixture of polar compounds having positive dielectric anisotropy, which comprises one or more compounds of the formula I:

• in which
• R is H or an alkyl, alkoxy, alkenyl or alkenyloxy radical having 1 to 15 carbon atoms, and,
• simultaneously, one or more compounds of the formula IIA and/or one or more compounds of the formula IIB:
• in which
• R′ is an alkyl or alkoxy radical having 1 to 10 carbon atoms or alkenyl having 2 to 10 carbon atoms,
• Y is F, Cl, a halogenated alkyl radical having 1 to 5 carbon atoms, in which, optionally, one CH2 group is replaced by —O— or —CH═CH—,
• in which
• R″ and R′″, independently of one another, are an alkyl or alkoxy radical having 1 to 10 carbon atoms or an alkenyl radical having 2 to 10 carbon atoms, and L is H or F, and,
• simultaneously, one or more compounds of the formulae III′ to X′:
• in which the individual radicals have the following meanings:
• R0:
• n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having 1 to 9 carbon atoms,
• Z0:
• —C2H4—, —C2F4—, —CF═CF—, —CF2O—, —OCF2—, —CH2O— or —OCH2—,
• Y3 and Y4:
• simultaneously H or F, and
• r:
• 0 or 1.