| 摘要 |
The invention relates to a liquid-crystalline medium based on a mixture of polar compounds of positive dielectric anisotropy, characterised in that it comprises one or more compounds of the formula I and one or more compounds of the formula IA in which R1, R2 ring A, ring B, L1-4, Z1, Z2, X1, X2 and a are as defined in claim 1, where the proportion of the compounds of the formula I in the medium is at least 18% by weight.
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