arXiv subjects

Sergey V. Krivovichev

Publications and source records attributed to Sergey V. Krivovichev.

3 recordsLinked to original sources

arXiv2026

Crystal structure, magnetic and resonant properties of decorated spin kagome system (CsCl)Cu$_5$As$_2$O$_{10}$

We report the synthesis and investigation of the crystal structure and physical properties of the averievite-like arsenate, $(\mathrm{CsCl})\mathrm{Cu}_5\mathrm{As}_2\mathrm{O}_{10}$. Just above room temperature, this compound undergoes a structural phase transition from the high-temperature trigonal $P\bar{3}m1$ $(a=b=a_0$ and $c=c_0)$ to the low-temperature monoclinic $I2/a$ phase $(a \approx \sqrt{3}a_0$, $b=a_0$, $c \approx 2c_0$ and $β\approx 90.6^\circ)$. According to thermodynamic and nuclear magnetic resonance measurements, it experiences a phase transition into a canted antiferromagnetic state at $T_N = 21~\mathrm{K}$. The density functional theory calculations place the energy scale of kagome exchange interaction parameter in $(\mathrm{CsCl})\mathrm{Cu}_5\mathrm{As}_2\mathrm{O}_{10}$ in between those in V- and P-analogs.

cond-mat.str-el↗

arXiv2023

The crystal structure of Pb$_{10}$(PO$_4$)$_6$O revisited: the evidence of superstructure

The crystal structure of Pb$_{10}$(PO$_4$)$_6$O, the proposed matrix for the potential room-temperature superconductor LK-99, Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O ($x = 0.9-1.0$), has been reinvestigated by single-crystal X-ray diffraction using crystals prepared by Merker and Wondratschek (Z. Anorg. Allg. Chem. 1960, 306, 25-29). The crystal structure is trigonal, P-3, a = 9.8109(6), c = 14.8403(12) A, V = 1237.06(15) A3, R1 = 0.0413 using 3456 unique observed reflections. The crystal structure of Pb$_{10}$(PO$_4$)$_6$O is a superstructure with regard to the standard P63/m apatite structure type. The doubling of the c parameter is induced by the ordering of additional O atoms within the structure channels running parallel to the c axis and centered at (00z). The O atoms form short bonds to the Pb1 atoms, resulting in splitting the Pb1 site into two, Pb1A and Pb1B. The structural distortions are further transmitted to the Pb phosphate framework formed by four Pb2 sites and PO$_4$ groups. The structure data previously reported by Krivovichev and Burns (Z. Kristallogr. 2003, 218, 357-365) may either correspond to the Pb$_{10}$(PO$_4$)$_6$O$_x$(OH)$_{2-x}$ ($x = 0.4$) member of the Pb$_{10}$(PO$_4$)$_6$O-Pb$_{10}$(PO$_4$)$_6$(OH)$_2$ solid solution series, or to the high-temperature polymorph of Pb$_{10}$(PO$_4$)$_6$O (with the phase with doubled c parameter being the low-temperature polymorph).

cond-mat.supr-con↗

arXiv2018

On the Origin of Crystallinity: a Lower Bound for the Regularity Radius of Delone Sets

The local theory of regular or multi-regular systems aims at finding sufficient local conditions for a Delone set $X$ to be a regular or multi-regular system. One of the main goals is to estimate the regularity radius $\hatρ_d$ for Delone sets $X$ in terms of the radius $R$ of the largest "empty ball" for $X$. The present paper establishes the lower bound $\hat{ρ_d}\geq 2dR$ for all $d$, which is linear in $d$. The best previously known lower bound had been $\hatρ_d\geq 4R$ for $d\geq 2$. The proof of the new lower bound is accomplished through explicit constructions of Delone sets with mutually equivalent $(2dR-\varepsilon)$-clusters, which are not regular systems.

math.MG↗