Magnetic and structural phase transitions of multiferroic boracitesM3B7O13X(M=

Abstract

The specific heat capacity of mostly single-crystalline samples of 21 boracite compounds M 3 B 7 O 13 X with M a 3d transition metal (Cr, Mn, Fe, Co, Ni, Cu, Zn) or Mg and X a halogen (Cl, Br, I) is determined. In combination with magnetic susceptibility data the magnetic ordering of the M 2+ ions at T N is investigated in detail. The fully ferroelectric/fully ferroelastic structural phase transitions at higher temperatures are measured by differential scanning calorimetry. In the Cr-Br, Cr-I, Cu-Cl, and Cu-Br compounds, previously unknown magnetic phases were found. Magnetic order in the boracites is characterized by the quantum and classical spin states of the M 2+ ions, a variable degree of structural distortion, orbital effects, and competing exchange interactions. The Cu-Cl, Cu-Br, and Ni-Cl boracites exhibit broad maxima of magnetic specific heat and of magnetic susceptibility above T N caused by low-dimensional or frustrated magnetic interactions. Co boracites display additional broad anomalies below T N originating from continuous spin reorientations and effective S = 1/2 ground states. Indications for spin reorientations are also observed for Fe boracites. New phases appear in high magnetic fields for some Co and Fe boracites, which is not the case for the Mn compounds. Stronger magnetic frustration is deduced for the cubic Cr compounds. For the latter compounds and Ni-I boracite magnetostructural phase transitions are observed.

Zn3B7O13Cl: A New Deep-Ultraviolet Transparency Nonlinear Optical Crystal with Boracite Structure

“…For the design of high-quality materials, one of the strategies is to modify and improve the classic materials by chemical reactions, which can not only overcome the shortcomings of the original materials, but also obtain better performance. Polar crystal structures are always decent templates, which have attracted more and more attention, due to their unique characteristics. − Thereinto, boracite structure (a chemical formula of M 3 B 7 O 13 X, where M stands for a divalent metal cation) with a new functional building block (FBB) (B 7 O 18 ) gets our attention, which is a multifunctional family with ferroelectricity, ferroelasticity, NLO properties, and so on. − Based on the consideration of the DUV transparency, alkaline earth metal cations became our first select for M. Thus, Mg 3 B 7 O 13 Cl crystals were investigated, which exhibit a short DUV absorption cutoff (band gap of 7.96 eV), a moderate SHG response (NLO coefficient near to that of KDP), and the typical ferroelectricity . The unity of the DUV transparency, NLO and ferroelectric properties makes Mg 3 B 7 O 13 Cl crystal a promising DUV quasi-phase matching material.…”

11B MAS NMR and First-Principles Study of the [OBO3] Pyramids in Borates

“…In this study, we investigated four synthetic borates of the boracite-type structures (Mg 3 B 7 O 13 Br, Cu 3 B 7 O 13 Br, Zn 3 B 7 O 13 Cl, and Mg 3 B 7 O 13 Cl) by use of multifield (7.05, 14.1, and 21.1 T) magic angle spinning (MAS) and triple quantum (3Q) MAS NMR spectroscopy as well as ab initio theoretical calculations. The selection of boracite-type compounds is based on the fact that the cubic varieties (also known as high boracites) feature the longest B–O bond distances among borates (up to 1.693(5) Å in cubic Mg 3 B 7 O 13 Cl , ), and low boracites contain a range of similarly long B–O bond distances. ,, Specifically, the diverse structures in boracites are related to interesting ferroelectric/ferroelastic phase transitions. ,,,, Cubic boracites (e.g., Mg 3 B 7 O 13 Br and Cu 3 B 7 O 13 Br) contain two types of four-coordinated B sites (collectively denoted as [4] B): three crystallographically equivalent [BO 4 ] tetrahedra (B1) and four equivalent [OBO 3 ] pyramids (B2) per formula unit . The O1 atom in cubic boracites is shared by four B2 atoms (Figure a), as such bond-valence requirements dictate the anomalously long B2–O1 bond distance of greater than 1.66 Å. , Trigonal Zn 3 B 7 O 13 Cl contains three equivalent [BO 4 ] tetrahedra, three equivalent [OBO 3 ] pyramids, and one [BO 3 ] triangle ( [3] B) per formula unit.…”

Lattice dynamics and a magnetic-structural phase transition in the nickel orthoborateNi3(BO3)2Pisarev1, Prosnikov2, Davydov3 et al. 2016Phys. Rev. B191100View full textAdd to dashboardCite

“…The very recent publication [23] gives a remarkable review of this group of materials. During the last decade, a large amount of studies was devoted to structural, magnetic, dielectric, and multiferroic properties of the rare-earth (R) oxyborates RM3(BO3)4, where M = Fe 3+ , Cr 3+ , Al 3+ .…”