Polar Polymorphism: α-, β-, and γ-Pb2Ba4Zn4B14O31–Synthesis, Characterization, and Nonlinear Optical Properties

Polar materials are critical for a variety of functional properties including ferroelectricity, pyroelectricity, and nonlinear optical behavior. Vital to developing new polar materials is an understanding of how the polarity influences the functional property, i.e., structure–property relationships. At present, structure–property relationships on polar materials have focused on materials with similar structural motifs. Interestingly, there are limited reports on the structure–property relationships of polar polymorphs, likely attributable to the challenge of synthesizing polar polymorphic materials. In this paper, a new strategy for the synthesis of polar polymorphs is presented. By employing this strategy, we report on the synthesis and characterization of the first example of a borate with all polar polymorphs: P1 for α-Pb2Ba4Zn4B14O31 (α-PBZB), Cc for β-PBZB, and P32 for γ-PBZB. In addition, powder second-harmonic generation (PSHG) measurements indicate that the polymorphs are SHG-active and type-I phase matchable. Structure–property relationships are discussed through theoretical calculations.