# Observation of a Polar Compound with Halide Ordering in the Compositional Series (CH3NH3)2Te(Br x Cl1–x )6

## TL;DR

Scientists discovered a new polar compound with ordered halide ions in a series of crystals, which shows piezoelectric properties.

## Contribution

The discovery of a polar compound with partially ordered Cl– and Br– ions in the compositional series is novel.

## Key findings

- The compound with x≈0.068 adopts the polar P63mc space group.
- The structure transitions through multiple space groups with increasing Br content.
- Piezoresponse Force Microscopy confirmed the polar structure with distinct piezoelectric domains.

## Abstract

Single-crystal samples of compounds in the series (CH3NH3)2Te­(Cl1–x
Br
x
)6 were produced
with counter-diffusion
crystal growth in silica gels, and new crystal structures are determined
using single-crystal X-ray diffraction. With increasing Br content,
the structure transitions from P3̅m1 to P63
mc to R3̅m and finally to Fm3̅m. The compound with x≈0.068 adopts
the polar P63
mc space
group, and the structure has partially ordered Cl– and Br– ions. The crystals of this compound show
distinct piezoelectric domains with different responses by Piezoresponse
Force Microscopy (PFM), confirming their polar structure.