International
Tables for Crystallography Volume D Physical properties of crystals Edited by A. Authier © International Union of Crystallography 2013 
International Tables for Crystallography (2013). Vol. D, ch. 3.4, p. 485
Figure 3.4.1.4^{a}Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, CZ18221 Prague 8, Czech Republic, and ^{b}Department of Mathematics and Didactics of Mathematics, Technical University of Liberec, Hálkova 6, 461 17 Liberec 1, Czech Republic 

Figure 3.4.1.4
Transmission electron microscopy image of the ferroelastic domain structure in a YBa_{2}Cu_{3}O_{7−y} crystal (Rosová, 1999). Courtesy of A. Rosová, Institute of Electrical Engineering, SAS, Bratislava. There are two systems (`complexes'), each of which is formed by almost parallel ferroelastic domain walls with needlelike tips. The domain walls in one complex are nearly perpendicular to the domain walls in the other complex. 