# High-Pressure Synthesis and Structural Studies of La, Sm, Gd, and Dy Chlorides and Chloride Carbides

## TL;DR

This study explores the creation of new rare-earth chloride and chloride carbide materials under extreme pressure and temperature, revealing unique structures like trans-polyacetylene-like carbon chains.

## Contribution

The discovery of trans-polyacetylene-like carbon chains in lanthanide chloride carbides under high pressure is a novel structural finding.

## Key findings

- Novel crystal structures of binary and ternary rare-earth compounds were identified using synchrotron X-ray diffraction.
- Trans-polyacetylene-like carbon chains were experimentally observed in lanthanide chloride carbides for the first time.
- Alkali halides showed enhanced reactivity under extreme conditions, leading to new chemical bonding and materials.

## Abstract

High-pressure synthesis
provides unique pathways to materials with
unprecedented structures and properties. Here we report the synthesis
and structural characterization of novel rare-earth (La, Sm, Gd, Dy)
chlorides, chloride carbides, and oxychloride phases obtained due
to complex chemical reactions in diamond anvil cells after laser heating
of rare-earth metals and NaCl at pressures of 39–127 GPa and
temperatures of 2500–2800 K. Synchrotron single-crystal X-ray
diffraction analysis allowed us to solve previously unknown crystal
structures of binary (La2Cl, LaCl, LaCl3, DyCl)
and ternary (DyNa2Cl5, Sm2ClC2, Gd2ClC2, Dy2ClC2, Sm19ClC18, Gd19ClC18, Dy5Cl3C, DyOCl) compounds. Significantly,
we identified trans-polyacetylene-like carbon chains
in lanthanide chloride carbides, a structural motif previously hypothesized
but not observed experimentally. Our findings highlight the enhanced
chemical reactivity of alkali halides under extreme conditions, uncovering
novel chemical bonding and expanding the landscape of potential functional
materials accessible through high-pressure synthesis.