Multianvil high-pressure/high-temperature preparation, crystal structure, and properties of the new oxoborate β-ZnB 4O 7

Abstract

In this work we report about a new oxoborate β-ZnB 4O 7 synthesized under high-pressure/high-temperature conditions from zinc oxide ZnO and boron oxide B 2O 3 with a walker-type multianvil apparatus at 10.5 GPa and 1100 °C. Single crystal X-ray structure determination of β-ZnB 4O 7 revealed: Cmcm, a=1085.0(1) pm, b=648.9(1) pm, c=517.3(1) pm, Z=4, R 1=0.0182, wR 2=0.0478 (all data). The compound exhibits a new structure type which is built up from linked tetrahedral BO 4-groups (□) forming a network. The most prominent feature of the tetrahedral network is that there is an oxygen, which is coordinated to three borons. The network exhibits channels formed from four- and six-membered rings running along [001]. The Zn 2+-cations are positioned in the large six-ring channels, whereas the channels built up by four membered rings remain empty. According to the conception of fundamental building blocks β-ZnB 4O 7 can be classified with the notation 8□:〈3□〉=〈6□〉=〈3□〉. The relation of the crystal structure of the high-pressure phase β-ZnB 4O 7 to the normal-pressure phase α-ZnB 4O 7 is discussed. Furthermore we report about temperature-resolved in situ powder diffraction measurements and IR-spectroscopic investigations on β-ZnB 4O 7.