# Orientation-dependent mutual crystalline and amorphous order in a single phase solid

## TL;DR

Scientists discovered a material that is amorphous in two dimensions but crystalline in the third, showing that order can vary by direction within the same solid.

## Contribution

A new material is presented that exhibits coexisting crystalline and amorphous order in different dimensions.

## Key findings

- The material consists of stacked 2D amorphous Nb-W-O monolayers with crystalline stacking in the third dimension.
- The amorphous layers follow the Zachariasen model for 2D disorder.
- This challenges the traditional distinction between crystalline and amorphous materials.

## Abstract

Amorphous materials distinguish themselves from crystalline materials by lacking long-range order while retaining structural order at the local scale (2–5 Å). However, the complexity in topological and chemical order prevents current characterization tools from fully unveiling the structure in disordered materials. Consequently, the nature of medium-range order in amorphous materials has remained elusive. The Zachariasen and crystal competing models have been proposed to describe disordered phases and have both been verified through synthesis and characterization. The main difference between them is thought to be whether the amorphous phase shows medium-range order. Here we demonstrate a form of organized inorganic matter that is amorphous in two dimensions, while exhibiting long-range order and a high degree of crystallinity in the third. The structure consists of periodically stacked 2-dimensional amorphous Nb-W-O monolayers without long-range in-plane order. The unique periodic and therefore crystalline stacking along one principal axis enables direct imaging and revealed that the amorphous Nb-W-O monolayers formed in agreement with the Zachariasen model for 2 dimensions. Our findings show that the gap between crystalline and amorphous materials does not only depend on medium-range order but can also apply to principal dimensions within the same solid.

Researchers report a solid that is amorphous in two dimensions but crystalline in the third, made of stacked disordered atomic layers. This shows that crystalline and amorphous order can coexist within a single material depending on direction.