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Thermal Expansion of the Low‐Temperature Form of BaB 2 O 4
Author(s) -
Guiqin Dai,
Wei Lin,
An Zheng,
Qingzhen Huang,
Jingkui Liang
Publication year - 1990
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1990.tb07626.x
Subject(s) - thermal expansion , atmospheric temperature range , anisotropy , crystallography , volume (thermodynamics) , materials science , crystal (programming language) , thermal , crystal structure , trigonal crystal system , negative thermal expansion , thermodynamics , chemistry , optics , physics , composite material , computer science , programming language
Thermal expansion of the low‐temperature form of BaB 2 O 4 (β‐BaB 2 O 4 ) crystal has been measured along the principal crystallographic directions over a temperature range of 9° to 874°C by means of high‐temperature X‐ray powder diffraction. This crystal belongs to the trigonal system and exhibits strongly anisotropic thermal expansions. The expansion along the c axis is from 12.720 to 13.214 Å (1.2720 to 1.3214 nm), whereas it is from 12.531 to 12.578 Å (1.2531 to 1.2578 nm) along the a axis. The expansions are nonlinear. The coefficients A, B , and C in the expansion formula L t = L 0 (1 + At + Bt 2 + Ct 3 ) are given as follows: a axis, A = 1.535 × 10 −7 , B = 6.047 × 10 −9 , C = ‐1.261 × 10 −12 ; c axis, A = 3.256 × 10 −5 , B = 1.341 × 10 −8 , C = ‐1.954 × 10 −12 ; and cell volume V, A = 3.107 × 10 −5 , B = 3.406 × 10 −8 , C = ‐1.197 × 10 −11 . Based on α t = (d L t /d t )/ L 0 , the thermal expansion coefficients are also given as a function of temperature for the crystallographic axes a , c , and cell volume V.